What has changed in horse racing that Triple Crown winners are so rare today?

I don't think nothing has changed, it is a tough task to put together 3 winning races at the classic distances. We had 3 winning triple crown winners in the 70's before that you have to go back to 1948 when Citation won the triple crown. today was the 134th running of the preakness but there have been only 11 triple crown winners.

There are some claims that racehorses aren't built like they used to be. If you look at Man o'War, who was a superb racehorse, even he was built more like a stock horse than a racehorse. A certain amount of endurance is needed to complete in, let alone win, a grueling series such as the Triple Crown.

Aside from that, it can be argued that it is just the normal ebb and flow of horse racing. There is no absolute reason why no horse has won the triple crown these last few decades, it's just the way racing is. There have been a lot of close calls (Real Quiet, Charismatic, etc) and some horses who have won two out of three. You also will recall the "dry spell" of triple crown winners between Citation and Secretariat.

However, I hope that I will see a Triple Crown winner in my lifetime, and I am certain that many horses running today are truly worthy, winners or not. :)

Moody, I think the answer to your question has many facets to it. Offhand, I would say that the number one reason why horses appear to be slower today than they were 30 years ago is largely due to genetics. The racehorses of today are among the most over and inbred animals in existence- it's a case of the law of diminishing returns. People are breeding for speed and to make a quick buck, NOT for stamina, soundness, or long term health, and sadly, THIS SHOWS. It's known in the scientific community ( which is NOT connected with racing for the most part) that the GENE POOL in the Thoroughbred breed has SHRUNK DRASTICALLY over the last half century or so- it's now down to about a third, or perhaps a quarter, of what it once was. As the bloodlines have become more and more concentrated, the incidence of preventable, hereditary defects has risen sharply- and to make matters worse, this has also resulted in slower speeds, because the animals simply can't run the way their ancestors did. These horses are also much more FRAGILE than their ancestors were, and much more vulnerable to injuries and death than the horses of 50 years ago. Then there's issue of the racing surfaces themselves- most of today's horses train and run on Polytrack, which is something that didn't exist 30 years ago- and all the Triple races are run on DIRT.Belmont, in fact, is mainly a sand track, because it's located on New York's Long Island. Being so close to the Atlantic Ocean natually means that the soil there is going to be sandy- that's a given. The difference in footing makes a HUGE impact on running style and on speeds. The increased distance of the Belmont also makes it a harder race to win- it's one of only a small handful of stakes races in the country which is run at that distance. We've been fortunate this year in that we appear to have a pair of horses which are real distance runners. Rachel Alexandra won the Preakness, yes, but she did so only narrowly. Another two strides, and Mine That Bird would have beaten her- and I strongly suspect that in the Belmont, these horses are probably going to end up challenging each other in an unplanned, unintentional, but VERY EXCITING match race- and they will decide for THEMSELVES who the real champion is. It will be interesting to see what happens when MTB finally gets close enough to RA to look her right in the eye.

There's another side to this, having to do with the fact that today there are many more races, and many more places to race, than there were 30 years ago. New tracks have been built in places where they didn't exist before, and these tracks make it possible for trainers and owners of nice horses to have the animals carve out decent careers without ever entering a Triple Crown race. That's what Nicanor, Barbaro's brother, is most likely to do- he'll skip the Triple entirely, because he's not Triple material- but he has the makings of a brilliant turf career. The advent of the Breeders' Cup series in the fall of each year has also not helped the Triple much, because the BC competes with the Triple in many ways. Plus, the Triple Crown is a grueling series, and horses which are actually up to the task of running 3 long races in a 5 week time span are increasingly rare now. I think that having the current TC events run as seperate races, the way they were originally, would actually do racing a service, in fact. It would take some of the pressure off the trainers and owners, because they could concentrate on each race itself as a seperate entity, rather than worrying about whether or not their horses had enough strength to complete all three. When these 3 races were first run over a century ago, that's exactly what happened- maybe they should give some thought to bringing that format back for a change. I think it would be an improvement over the current situation, which is too demanding in a lot of ways.

That's my take...

Way back when horses were used to race every 2 weeks and sometimes once a week. Now these horses race every month or two. Then they're faced to run 3 races within a month and a half and they can't

Where to start on this one, since 100 people will have about as many responses. In my view the breed is not as sturdy as it has been in the past and Thoroughbreds are mostly bred for speed (sprints) and not developed for "classic" distances. And so many great bloodlines have been lost to overseas breeders that there has been a cumulative effect over the past 30 years.