1) there is going to be a lag between the great on the field performance a 12-1 season is and the expected recruiting boost because most of the recruiting for the kids who just committed was done following the '17 season. The kids who's heads were turned by the '18 performance are the ones who will commit next cycle (unless '19 is a down year and turns them off).
2) '17 is only a good year when you look at it in a vacuum as it was 10 wins, but actually '17 was quite a disappointing year (based on the first 3/4 of season) that was only saved from being another 4+ loss season capped with a bowl loss, by a once in a lifetime (individual effort) one handed catch and score.

As time passes memory will fade on what a let down 10-3 was that year and if Kelly keeps stacking 10 win seasons on each other a couple years from now no recruit will be aware of that disappointment and will only see 4-5 straight 10+ win seasons (hopefully) and then we'll be feeling the recruiting swell reflecting our on the field performance.

However, to think the '17 season was good enough to impress the class of elite recruits who just committed, requires some serious eye squinting that unbiased recruits looking for the best opportunity to win a lot and go pro just aren't doing.