Probably a smart move. Writing and mailing a letter takes a lot more time and effort than a phone call or comment online. If a person took the time to write a letter, they're probably worth taking the time to respond to.

you can get a lifetime fan just by replying to a letter - like you see here. That's a very effective marketing.

I got a rejection letter once from a company I submitted my resume to (online) and I still remember that and in a positive light even though it was a rejection.

Now they just ghost you even if you went through 5 rounds of interviews and spend a bunch of your time.