The lack of shirt is simply explained by the fact that it rips during the transformation and falls off in tatters. The fact he puts his labcoat back on is because he's more than likely very tired of being objectified and wolf whistled at whilst shirtless and wants at least a little modesty.

@AllTheEpochs Except they do it even when he stays skinny in a lot of the art. I am aware of all the implications, but the shirt is under the labcoat and even in the comics there are panels where his shirt is removed without ever taking the labcoat off even post transformation lol.

There are also instances where he has his classic black shirt and it's fine, but the labcoat gets torn up, or the pants do but only below the knee where it doesn't grow out enough.

At the end of the day it's always been an artistic decision, I just always found it funny how all over the board it can be. I wouldn't take it as some form of -actual- criticism, just a fun observation.