The 5 star pro style QBs often struggle in college because they are asked to run a more spread and mobile style of offense than they would be asked to run in the NFL. They washout in college as a result.

Oddly, some of the lower ranked pro style QBs end up making it better in college because they play at lower tier schools and end up being a big fish in a small pond and get noticed.

It is just a theory of mine. I could be full of shit -- like I am on most other things.

Another theory is a lot of the highest ranked QBs get stacked up at the same colleges, so only a fraction of them start and others have to transfer and that often blows up the flow of their college carrer.

HS quarterbacks are often throwing to receivers open by 3 steps. Tighter windows, closing speed of the defensive backs, and more sophisticated defenses may trump raw talent.

Typically college QBs face a better rush, which also forces quicker decision making

The ability to read defenses both before and after snap is key to later success, but less so in HS.

QBs who are 5* in HS have raw physical talent and success against lesser opposition.