That and the fact that college kids have yet another 1 to 3 years of training under their belt.
As to the OP, from what I've read, they do not train like college runners, let alone Pro runners. They do take it seriously, but the volume is way lower.
They are certainly not the only HS athlete's to take their sport seriously. They have a number of things in their favor: a good coach, good teammates (current and past), and talent. I'm sure there are other reasons as well.
Take any one of them out of their environment and it's hard to say what they would do. My guess is Colin would still be a 800/1600 stud. Leo and Lex would still be great at XC. Guessing times is impossible, but it would likely be slower.