Re AZ, last year my son played in the junior and senior fall classics . . . a few factors may be in play to drive D1 attendance at the Senior Classic:
(1) The Senior Fall Classic weekend also has a JUCO component: https://azfallclassic.com/jc-all-star-series/ so it may be that the D1s are in town to see some of those players
(2) The Senior Fall Classic has some sophomores and juniors playing -- I recall specifically seeing PAC12 schools at a game last year, but they were watching an underclass scout team and specifically a sophomore pitcher
(3) There are always pop-up uncommitted seniors -- last year there was an unranked SoCal RHP sitting 92-94 who got a lot of attention. (He ended up going pro)
(4) The senior and junior classics are back-to-back weekends, so some of the out-of-state D1s come for both.