There were a lot of modems better than Hayes, but Hayes did create the AT command standard, which wasn't a real standard, but better than nothing. A modem that didn't answer to at least the basic Hayes commands was a headache.
Then there were USRobotics... Sure they had some of the first high speed modems. That is they were faster than 1200 or 2400 baud. But they did it using their own modulation techniques. So to get the high speed connection you had to have a USRobotics modem at both ends. A friend of mine set up a bulletin board system, paying the phone company for extra phone lines just for the BBS and USR huge discounts on the modems. They figured that if they got enough modems out there on bulletin boards the users would buy enough USR modems to make up for the discounts.
And this business model worked, for a time. Though USR wasn't the only manufacturer with fast modems they were the ones you were most likely to encounter when calling into a BBS. I won't say the others didn't try to offer discounts, but to a BBS operator it was a good idea to have the modems that the users was most likely to have. And USR more or less owned that market. Once V.32 modems got cheap USR saw dwindling returns, and V.90 more or less obliterated their business model. When you could choose from twenty or so brands and they all performed similarly price was often the deciding factor, and USRobotics initially tried live on their name and keep their prices up.