I would guess that a large majority of the users who utilize these services are petty criminals who are laundering small amounts of stolen funds.
Chainalysis say only 8.1%, https://e-cryptonews.com/chainalysis-most-mixed-bitcoin-not-used-for-illicit-purposes/.
That point aside, you have to assume that government agencies such as the IRS have likely already setup their own mixing services as honeypots or are monitoring mixing services to go after any large transactions they are able to trace (which is easier than you think).
You don't need to assume, mixer which use CloudFlare can be considered as honeypot and government already hire blockchain analysis service (such as Chainalysis) to trace all Bitcoin transaction. But how accurate their service is different case since each mixer have different way to break the link.