Privacy concerns, anyone?
If they substitute email, will the email be encrypted and signed? Will they set up TLS tunnels with everyone receiving such emails? Though not exactly secure, fax is still better than email.
(I once worked for a company that made inline encryptors for fax machines, complete with PKI. Very, very few people bought them despite their reasonable cost. We even had a sales demo of intercepting a fax, altering the sums, and sending it on. Usual response: that's not right!)