There are 30 MLB clubs which employ area scouts who have a single job: identify players - in their area -who have at least one single MLB potential tool and sell that player to his organization. A scout who doesn't identify the talent in his area will not be employed long (and to extend the area scout's reach, the scout will develop a network of coaches [travel, HS, CC and college] and associate scouts who scour the area looking, looking, looking). (And scouts get a little bit of extra money for every kid in the area signed by the team; gets a little bit of money each time the kid is promoted; and a little more more if the kid goes all they way.)
A coach is able to recuit - in part - because he is able to develop his players to reach the next level. He sells new recruits on the idea that if they attend his program, the pros are waiting. (It is debatable whether most coaches really know how to develop, but that is for another thread.)
If word got out that a player was being "hidden" to the player's career detriment, that coach would not be long in his job; he just couldn't successfully recruit.
I know kids who have been drafted (in single digit rounds) who were total college busts - but somehow were seen, evaluated at the local and national level, and got drafted. I have known kids who were perpetually injured who got drafted; I've known kids who were known to need TJ get drafted. I've known kids who had a single season of good summer ball get signed right out of summer ball. While surely there is a kid here and there who is missed, the entire baseball systems' incentives are aligned to find players with at least one potential MLB tool.
Now, I have also seen kids who, for example, have starting pitcher stuff be turned into closers and thereby not be scouted as starters in college. But I have seen those same kids have lots of innings available for summer ball - where they are starters and are scouted as such.
They system finds virtually every kid who is evaluated by a scout as having a potential MLB tool. On the other hand, with 95% not making it all the way, it's really good to have a plan B - whether playing days end in college or MILB.