AFAIK, one reason for that is that AT&T was the monopoly provider of telephone equipment. They didn’t have to compete with anybody who might undercut them for price. In addition, people often rented their phones, paying a small rental charge every month. That meant that AT&T built the phones to last. They were extremely solid because AT&T didn’t ever want to have to replace a phone that someone was renting.
AFAIK, one reason for that is that AT&T was the monopoly provider of telephone equipment. They didn’t have to compete with anybody who might undercut them for price. In addition, people often rented their phones, paying a small rental charge every month. That meant that AT&T built the phones to last. They were extremely solid because AT&T didn’t ever want to have to replace a phone that someone was renting.