That 90% is for both of the two biggest DMSes, CDK and Reynolds & Reynolds. Both DMSes have been around since the '70s or so, so they're probably considered a safe option by a lot of dealers.
Switching DMSes is likely disruptive, but is still pretty common. We've had dealerships do it every now and then.
This will also be interesting to see how it affects their their long in-development and repeatedly stalled Fortellis product. They are attempting to release it as a DMS agnostic solution which I did not think that other DMSes will gravitate to just because it comes out of CDK. This attack is just another reason for a competitor DMS to not use it.
Does Fortellis even accept other DMSes? I've dealt with it a bit to integrate with eLeads (now CDK CRM), but there didn't seem to be much on there apart from CDK's APIs.
This is for software programming. Their salary ranges are also unbelievably low and they avoid interviewing anyone with even moderately strong qualifications (which would be considered "mediocre" qualifications in any tech hub).