Also the advertisers were (for no obvious reason) among the heaviest users of some obscure whacky DNS software that implements just barely enough of the specification to answer A queries from Windows clients.
If you send such a server pretty much anything else, such as an AAAA query, it either silently discards the packet or it returns a NXDOMAIN for an unasked A query. Probably this was sold to the user as a "security" feature, the practical upshot is that lots of perfectly good implementations will stall when trying to connect to some of the popular advertising sites.
You would think that this was something advertising companies would want to fix, but it seems not. Somewhere along the lines "we make advertising" plus "people are annoyed by advertising" became "it's our job to annoy people" and so there was no interest in fixing the problem. I don't know if it ever got fixed at all.