Except for the fact iMessage is well known for its RCEs as well: search for "iMessage RCE" you will find them. Furthermore (this may not be the case anymore),

Except for the fact iMessage is well known for its RCEs as well: search for "iMessage RCE" you will find them. Furthermore (this may not be the case anymore), iMessage is more privileged than other apps and so once exploited an attacker has a far greater reach.