Most particularly, because their corrupted activities and policies have little adverse effect on the general population - which remains largely independent and self-sufficient.
Most Thais have conditioned themselves to be rather indifferent about the usual and historied shenanigans and skullduggery.....unless such delves into their everyday lives [which it doesn't].
Pay attention to the average Thai community and one will find that the local political comings and goings are much more important to their lives and concerns. It might be extended local mafia, but it's their own extended local mafia.