So, all three of my gliders' tails are not big and fluffy like I see in so many glider pictures. They are full of fur, no bald spots, but all skinny. Is it genetics? A colony preference to keep the tails groomed down? Am I doing something wrong? Or am I just nuts?

It can't be the season, I've been observing their tails for over 5 years and they really don't change much.

I know it isn't diet. I feed Critterlove with salad #3 (their preferred salad).

https://photos.app.goo.gl/Qx62QUZ3iqg9okkbA

Their tails look good.
You may be thinking other fluffy gliders have fluffier tails but an over weight, chunky glider has a fat tail which could be making the tail appear fluffier.

Come on Feather, you just like looking at my little man's tail! Lol!!! JK!!!!

So they do store fat in their tales like other mammals do?

Yes, Conner had a fat tail. It probably caused some of his three amputations.