7.3% sounds really low to some, but it's about right.
There are a lot of "D1 or nothing" kids who self select out. Alot of those kids with that mentality have plenty of talent to play D2 or D3 but they prefer the big D1 college experience and/or just don't love the game enough.
Injuries, especially arm injuries, takes another portion of players out of the picture.
Then you have to factor in that, in a huge portion of the country, high school Baseball is very mediocre, and there are a ton of high school teams. There just aren't a huge percentage of high school players from Wisconsin, Alaska, North Dakota, South Dakota, Idaho, Montana, etc that go on to play college ball.
The fact that there is such a small amount of scholarship money in Baseball is another factor, especially for multi sport athletes. The reality that a kid could be looking at 25% of a scholarship in Baseball vs a full ride in Football, Basketball or even Golf (!) takes even more players out of our sport.
Then you factor in drugs/drinking, bad grades, attitude issues, troubles with the law, etc, as well as simply those who are unable to afford college.
If anything, 7.3% sounds high to me