As usual those exploits require the management interface to be open to the internet. Which you should never do to begin with on any router, and it isn't setup that way by default. Mikrotik is fine to have on WAN if you don't purposely make it insecure. Even Cisco has had similar vulnerabilities when you configure them in such a wrong way.

And yet people still do it, hence the botnets...

Yes, but my point is that there is nothing unique to Mikrotik here that makes using them on WAN a bad idea. Configure an Ubiquiti, Cisco, Aruba, Palo Alto, PfSense, etc in the same way and you're inviting trouble.