I’d say calves are the number one bodypart people where just say “LOL, well I tried, but nuthin’ works.”
Genetics, in the sense of unique individual muscle origins and insertions, are a huge factor. Mind-muscle connection and exercise choice/technique is probably the next most influential factors.
Dennis Wolf was notorious for having “high lats” and no amount of Meadows rows would’ve filled out his “lower lats” to any major degree because there was nowhere for the muscle to go.
For something like the upper pecs, I’d say a large part of that (no pun intended) is the muscle-section size. Think of how relatively small the upper pecs are on the body, then think about how muscle (actual muscle, not total bodyweight) most people gain in a year.
There’s only so much it’s gonna grow without spending investing a ton of time into figuring out how to target it and then getting lean enough to discern upper pecs from moobs.
We also kinda need to realize that this type of bodybuilding-focused perspective matters much more to you than to the majority of other people. Unless there’s a glaring discrepancy or shortcoming, a truly jacked dude is going to look jacked whether or not he has a quad sweep, a full upper chest, or whatever fine-tuned criteria we’ve pulled from competitive bodybuilding.