Well it depends what you're talking about, by "you guys". Me, I bulk and do exercises with one goal in mind, strength and conditioning because I am into martial arts.
If you mean you guys, bodybuilders, fitness models, bodyweight lifters, weight lifters, CrossFit athletes, they all have a different type of training.
As for fighters, boxers, muay thai fighters, they have indeed a more developed upper body in general, and thinner legs. It's just due to their training, and what they decided to focus on.
There are also fighters, that come from All American wrestling, or freetyle wrestling, that have huge thighs, like Tyron Woodley, because of the amount of grappling exchanges, and the specific training.
My legs were bigger because of playing soccer since a young age, and also genetic. In general you can train you legs, making sure that you don't end up with "tiny legs" as you mentioned 😁 . That's why gym freaks always say : Never skip Leg day!
Thanks for the clarity. I think I need to secure a gym instructor who understands all these before I can hit the gym.