It will, ther just isn’t much call for it. I used to be in manged services and for some clients analog backup was a requirement, but you typically want those using a POTS line because they are less susceptible to power and network outages. FoIP is a thing, FAX shares the same basic principles, and there are protocols and codecs specifically tailored to provide better FAX transmission reliability.

Look up PCM, It’s pretty interesting if your into that sort of thing, and there is plenty of room to chase the rabbit.