I fail to see how wearing a uniform aids you in any way, shape or form during training. Unneccessary corporate branding and pretentious bollocks.
Fine, if you're a pro pilot you wear a uniform. The public expect to see a smartly turned out crew flying their aircraft. But for training? Load of ****e in my opinion. A uniform doesn't help you fly the aircraft any better.
I don't fly for a living, but I do have a well paid job which requires professionalism. If I have meetings with outside execs and other such important folks, fine, I'll wear a suit as in those instances the impression matters. When I've got an easy day and I'm just sat around in the office, I'll put on a pair of jeans and a shirt. Uniforms for the sake of uniforms is stupid.