why is star wars meant to be watched 4.5.6.1.2.3?

It isn't meant to be watched 4, 5, 6, 1, 2, 3. It is just that 4 5 6 came out first and then the creater went back later and did 1 2 3 when he realized that there was a lot of backstory to tell. The chronology is 1, 2, 3, 4, 5, 6.

Because there are plot twists in the original that would be ruined by the inferior prequels. It's much more rewarding to find out that Vader is Luke's father when they're dueling in Cloud City, instead of finding out by watching him as a whiny little snot.

And I hate to break it to you, but Sheldon and Leonard are TV-lite dorks. Meaning that they're superficial caricatures of nerd culture, rarely saying anything on the show of real weight. My favorite example is when Sheldon explained the Higgs Boson particle to what's-her-face. He never once actually explains the particle, instead providing an idiotically shallow history of it. Ugh. I swear, everyone thinks they're a geek these days, but virtually no one has the creds. I'm a billion times geekier than such pretenders, and I don't consider myself a geek.

George Lucas thought that 4,5,6 since it shows Luke winning would be better received by the public. Plus when the 4,5,6 were made the special effects weren't what he need for 1,2,3 at the time.

4.5.6.1.2.3, is just the order in which they were released. It makes sense to watch it 1.2.3.4.5.6 because that is the chronological order of the series.