Email is pennies per thousands.
Phone calls are cheap especially for nonconnected or robocalls (which would cost for a postal contact).
Postal mail costs $0.50 US in postage alone. The full-up cost of a mail campaign is often several dollars per mailed item, though in bulk, and with bulk rate, I believe it's closer to $0.40 (postage plus a few cents for paper and envelope).
That would cover many thousands of email contacts, possibly nearly as many phone/VOIP attempts.
And the systems required to successfully and accurately generate a postal response on request are also high.
Low-cost systems are high-fraud systems.
I was disappointed that no alert was sent through the banking app. That would be the most secure option but is explicitly disallowed in the notification settings.
They can include information in the letter they can't include on a phone call, as the mail service is performing the authentication.
My health insurer won't talk to me on the phone without me confirming identity, even if they called me, but they'll happily mail the info.
Never call the number off the letter, though.