The above numbers are mostly about who has the most players who are paid premium contracts.
It's no secret that most of the above put out more 1st round draft picks than we did in the last decade or so, and that those rookie salaries are going to occupy a good chunk of the above.
Trevor Lawrence, for example, already accounts for $70+ million of the above Clemson number, and he hasn't even been in the league that long.
Tua Tagovailoa and Jalen Hurts have a similar number, having earned over $70 million each as well (accounting for a large chunk of Alabama's money, and Oklahoma's money, respectively).
The ones playing their second contracts are contributing a lot as well, but here again, with a lot of those schools having more success at putting out early round draft picks, even before 2015 (those guys became the second contract guys at the early part of that last decade), they're going to have the lion's share of such premium contributors.
Right now, if you look at the contracts of Quenton Nelson, Mike McGlinchey, Ronnie Stanley, Zack Martin, Joe Alt, Stephon Tuitt, Golden Tate, Harrison Smith, and the nice signing bonus paid to Jaylon Smith, that's the vast majority of the above figure.
The other significant contributors would be Romeo Okwara (had a nice final contract), Jerry Tillery, Nick Martin, Kyle Rudolph, Cole Kmet, and maybe Tyler Eifert.
I know that I didn't include everyone, and that I missed some significant contributors, but those 15 players mentioned above take up 90%+ (my best guess) of the money pool mentioned above. They've all have / had good careers.
In the next couple of years, we'll definitely climb that ladder, since Kyren Williams is rumored to signing a new contract that pays him 10+ million / year, and Kyle Hamilton is in a similar boat.