Making the body look bigger can make the penis look smaller by comparison if you aren’t doing PE to make it grow too. Like Lee Beast said, with 32” quads, even an 8” penis will look small by comparison.
Supporting what was said about testicular shrinkage too. Depending on the gear they use the testes will shrink when bodybuilding drugs are used. In my opinion, deca is the worst offender. But with proper use of ancillary treatment and post cycle therapy, it’s not even much of a concern these days for those who are educated enough in what they are doing to avoid the worse side effects.
About the weight gain and weight loss. If you fat pad gets bigger, you will have less visible, external penis. When you lose it, you have more external, visible penis. When I was 300lbs I had a 1” flaccid sticking straight out of the fat sitting on top of my balls that were pushed forward by my fat legs. At 170lbs, before PE, the 2.5” that I had looked much bigger. I’m still glad to have 4+ flaccid now though. No one ever sees it but my wife and she doesn’t really care what I’ve got hanging although she does like the erect gains when we are using it. However, it’s easier to pee now and I no longer hit my hand with it sometimes. Interestingly now at 200lbs with a low body fat percentage, it doesn’t look that small compared to how it used to be. Must be the fact that the fat pad is smaller than ever before that gives this illusion.