I don’t think we like it much either 
I’ll try to communicate what I’ve picked up about displayHtml, although it might not be 100% complete, so other blockcerts members can correct me or put in their 2 cents.
There’s trade offs and pros and cons to it. Providing certificates that look the same across all devices, browsers, and apps is a hard thing to accomplish, while keeping the integrity and verifying that the way it looks to a verifier is the way that the issuer designed it. For certificates that are typically physical and visual, there’s value in providing the same visual experience in digital form here as well. Graduation records and the designs that go into them are the big ones that come to mind.
I think the reason it’s not in cert-tools right now is because we didn’t want it to be part of the standard, at this time. It’s a weird situation, especially since we currently rely heavily on displayHtml. I think we do want to improve this, and there’s talk in the verifiable credentials community on how to handle verifiable displays.
IMHO, it should display displayHtml when it’s there, and provide a standard display otherwise.
I agree. In fact, when a couple of us talked about it today, we thought it did provide a default view. Since we mostly deal with certs that have displayHtml, it’s not something that we test or run into all that much.
Have you experienced what happens when you try to import a cert that does not have displayHtml?