Aren't most of the Tor exit nodes widely thought to be run by government agencies? People thought that was true at a security firm I used to work at. I wouldn't be surprised if Tor was a honey pot designed to catch people doing nefarious things.
Governments also run a lot of relays and exit nodes for a similar reason. Not to make it easier for themselves to identify traffic. For no one actor to have a majority of nodes, which would make it a lot easier to identify traffic.
So far, the high profile busts involving Tor all involve some other weaker link in the chain, such as traffic analysis[0], a CI, a targeted sting operation. etc.
If this is the case and your hypothesis is true, then it appears to be unnecessary on their part, since all the folks they're prosecuting are those for whom other evidence is more readily available.
(Before someone replies with "parallel construction": the point of parallel construction is to use methods that are easy but illegal to obtain evidence that can be used to help find "legal" sources of evidence that would otherwise not be easy or feasible. That doesn't really apply here, where the illegal (or in this case, secretive) method is more work than the "official" method).
[0] e.g. that case a decade ago where a student called in a bomb threat using Tor, and the university was able to determine that exactly one person on campus was using Tor at that time - not by compromising Tor itself, but because Tor traffic is detectable by ISPs.
(If I recall, the Snowden files also contained a claim by NSA that they could not break Tor.)
After all, with a VPN you get to see source and destination IPs, username, e-mail, payment information, and maybe they even download your connection tool and run it as root.
If you control the exit nodes, you can snoop on the content, even if you don’t have the destination. The goal for governments isn’t catching crime, it’s spying on secrets. Same way WikiLeaks was supposedly started by snooping on Tor traffic.
Anyone browsing non-SSL sites through Tor is a fool, because malicious exit nodes are well known to exist, doing things like replacing bitcoin addresses in unencrypted web traffic. You don't need to be the NSA to benefit from doing that.
And, again assuming this is true, how would any other technology protect you better?
Especially people working at "a security firm" should know that security is not black and white, but has many dimensions to it.
And then, here we are talking about diversifying relay operations, so even if you believe the rest of the network to be totally compromised, it would still add some net benefit, no?