How do ISPs enforce modem compatibility?

I was reading about purchasing a modem for use with my local ISP and noticed that they produce lists of compatible modem models.

How is this compatibility enforced, if at all? Is there some technical mechanism by which they could tell if I'm using an "unapproved" modem? Or, is this really just more of a marketing thing to ensure people don't blame their ISP for their bad hardware?

From what I previously understood, my ISP will just hand me a DHCP lease once I give them my MAC address over the phone. I looked a little bit into whether it's something with the DOCSIS standard, but Wikipedia claims that all versions are cross-compatible: https://en.wikipedia.org/wiki/DOCSIS#Versions

There are some vendor codes that you can pass in a DHCP request, but I'm not sure those would be used for identifying very specific models of hardware.

I thought I'd post this here instead of /r/homenetworking because I'm more interested from a technical standpoint about how the ISP could possibly enforce their approved lists. I'm a little surprised that I haven't been able to find anything about how they restrict modem types. A lot of people claim that you really need to get a "compatible" one, but I have no idea why.

I will likely be getting one on the compatibility list anyway, I just am really curious how they'd tell if I'm using a compatible one.

Thanks!