Ok, to put it simply.

Absence of evidence is not evidence of absence.

If an event happens, and multiple previous times that event happened a cause was identified. It is reasonable to suspect the same cause was responsible this time.

It does not give proof, but it does give reasonable suspicion.

Fair, I misread the GP's post, sorry. (For some reason I thought they were claiming that the companies that colluded in the past went bust, leaving only the non-colluding ones.)