Why do people wear sweatshirts and sweatpants while at the gym? I would think it would be to sweat off some pounds but I see guys trying to put on the pounds wearing them too.

Just something that crossed mind.

less reps, more weight. Eat more too.

Do 4 sets of 6-8 with heavy weight.
Eat early(first thing when you wake up) and late(last thing before going to bed).

I have a routine to go to the gym before work. It's just part of waking up and morning tasks. Takes away the need to stay motivated.