They always have been, but no one likes it because it's not predictive. The reason you have to look at multiple years at once is because if you have a guy who's a junior in year X, and he plays another year and gets drafted as a senior in year X+1, he is still almost assuredly a better player and bigger impact on the field than a guy who is a senior in year X and doesn't end up in the NFL at all. If they didn't underachieve due to coaching (see, FSU this year), a team with 5 NFL players this and 5 NFL players last year is probably better than a team with 7 this year and 0 last year. That 1-year difference is safe in most cases, but there are definitely players who are better as sophomores or even freshmen in a few cases than seniors whose football careers are over at the end of the season. That's why recruiting is so important, having even 1 bad recruiting year can throw off that layered depth of next-level talent.