Why shouldn't you wear shorts when horseback riding?

You can ride with shorts, just avoid brush on the trails. If you are a good rider and have a comfortable saddle you will be fine.

According to me, it creates problem during the riding. Sometimes we feel etching on the legs, so we cannot concentrate on the ride and get chances to harm yourself.

Its only fun bareback at the pond when its 90 degrees

You can. I used to ride bareback, in a dress with the skirt tucked up. It depends what you and the horse are used to.

If you think that doing this is a comfortable way to ride, John, then by all means try it. I guarantee you that after the first time, you'll never do it again. You'll be so sore and your legs will be rubbed so raw that you won't be able to sit comfortably for a week. But it's up to you. If that's how you want to spend your time, don't say we didn't warn you about it.

As others have said to stop rubbing on the saddle and getting your skin pinched by the Stirrup leathers

In reality more experienced riders can and do ride in shorts

They either do this with a saddle but more often without the saddle.

I have ridden in shorts both with and without a saddle

Your bare skin rubbing against the saddle and getting pinched in the stirrup leathers is going to hurt.

If you go trail riding, those thorn bushes your horse takes you through are going to tear into you, and he's not going to stand still and let you remove them - he's gonna whirl at speed to make it worse.

But hey, if you wanna wear shorts, go for it.

OUCH!!!

If you try it once you'll KNOW why.

To avoid blisters, you genius.