Guessing? I just told you he's not exceptional at anything. If you disagree with that, I'd like you to elaborate on that and tell me what he's so great at. IMO he has a good base level, but what trait will he suddenly develop to a level that will make him world class? He doesn't have exceptional pace, acceleration, power, carrying ability, ball striking, passing, crossing, decision making, 1v1s, technique, athleticism, physique, creativity, etc.
He has a good base level to be a solid Premier League level winger with good output. He's also a hard worker, and he's relentless, which is probably his best trait.
But what exactly is going to make him explode into a world class player? I don't see anything in his game that's outstanding, or anything that could develop into outstanding, even if it isn't at that level right now.
It also says a lot that you are like the 5th poster I'm having this conversation as well, and no one has answered my question yet. It's always just his age, the stats, the Puskas award, etc. that gets brought up as to why we should keep him or why he has "massive potential".
He's a good talent, but he's not a special talent. Mainoo is a special talent. Yoro is a special talent. Even Hojlund can be coached into a special player because he has the tools, and the stuff he doesn't have yet can be taught and coached into him. Rashford and Martial at 20 were outstanding, and very much special talents. Shaw as well at 20 before the leg break. You could see that based on ability, the sky is the limit for these kinds of players.
Garnacho is nowhere near these guys at the same age. And players never outgrow their profiles. His profile is just not valuable enough to be considered an unsellable asset and if a club offers 60m for him, it's probably around what he would realistically cost at his peak, which he hasn't entered yet presumably...so why wouldn't you sell him?