You have an event where thousands of boozed up and possibly coked up individuals are trying to get home and you pack them in like sardines to a three coach train? Madness, I witnessed three fights break out in the space of 20 minutes
Looks from RTT like service was solidly 4-car all day yesterday. I expect they're very careful to avoid diagramming a 3-car on race days at least. The cancelled diagram ("planning error") was 1620 to Cambridge (too early for racegoers) and the 1709 to Ipswich (not the bigger flow and also before even the penultimate race).
Newmarket races is mostly attended by car, and is set up accordingly. I attend at least annually and although I try to go to places by train if possible, I would never consider doing Newmarket by train!
You just can't move vast amounts of people emerging from an event on the railway equivalent of a minibus working a B road with passing places.
Stagecoach East should take more of the blame for this by withdrawing the weekend service on their Newmarket to Cambridge route 11 a few years ago. Those buses were always busy after meetings and much easier to bolster service. The replacement local authority subsidised Tiger service, M-F, is a poor substitute.