A few years ago, I've presented a statistic on Bitcointalk about mixers and illicit money: Chainalysis research reveals: only a small percentage of mixed coins are illegal
Let's have a look here:


Source

So, according to Chainalysis, only a small percentage of mixed funds are from illicit origin. I'm sure, the numbers don't have changed much (it's data from 2020).

ChipMixer's problem is very simple in my opinion: After operating since 2017 (for 6 years) it was known by many scammers, so recently, a lot of hacked, stolen or extorted funds went to ChipMixer.
But such high numbers for illicit funds are obviously specific for ChipMixer because it was known by scammers after operating for such a long time (which we didn't know until it was taken down).
It might look completely different for average mixers (similar to what Chainalysis found out) and only a small percentage of mixed coins are illegal.