One reason committed kids are in mid-season form in winter of their senior year is the draft.
Last week I sat in a backyard where several scouts gathered at the local guru's house to watch pitchers; mostly older pro guys who were looking to get picked up (a sad perennial story for another thread). But, mixed in were HS seniors who were also throwing and getting gunned.
No question its early (though colleges have or will shortly start seasons), but the HS season is over quick (maybe 10 starts for a pitcher).
Scouts need to first identify the pool of players to be seen, see each several times to begin an initial ordering of players, - for single digit prospects - word and video is sent to home office so that HO can decide where the top guys in scouting go (e.g., cross-checkers, asst gms, and even higher for top round potential). With only March - late May to evaluate, there's lots to do and little time to do it. (You might say the clubs are making their lists and checking them twice.)
A single digit HS pick needs to have miltiple levels of eyes on.
Indirectly related, I have seen GMs, cross-checkers, and heads of scouting, scout the very first game of the HS season (scouting prospective 1 - 2 round picks) and have seen those kids completely fall off the draft table after a few early season looks.
Now, there's always going to be room at the draft for the 95 mph guy who cranked it up later in his HS season; but the early bird catches quite a few worms.
(I watched Max Fried amd Lucas Giolito (sp?) throw at a mid-January college HS tournament several years back. One sat 94, the other 97 - in January! Both first rounders; one needed TJ immediately; the other a few years later.)