Davez, the only reason I can think of with the longer races is that the luck factor seems to be stronger. There is the possibility that the race may not be truly run which can lead to "sprinters" or badly weighted horses winning in a slowly-run race. Or again, in a very fast-run race, it could provide an advantage for the backmarkers and consequently a disadvantage for the leaders. And these types of races have in the past often led to uncertainty for most of the jockeys.

Maybe with Maidens, they don't have enough race starts, if any, to use as a reliable guide for the form. And maybe also any unsuccessful horse no matter how good or bad it is, or its age, can lead to a hodge-podge/lottery-type race?

One selection today which happens to be in a Maiden race;
Almost system
Gold Coast R3 no.12 - Sweet Venture