Unlike computer companies, the local phone companies are not used to being leaders in technical innovation. Management decisions are made by people who have been in the phone business for decades. These people are most familiar with POTS, and anything else is a special service that requires support specialists and special, high prices. From top to bottom, the phone companies share a long-standing culture that resists technology changes. Of course, increasing competition is forcing them to change, but they're resisting the move to competition, too.
Profitability is the primary motivation for most companies, but for some it is the only motivation.
The phone companies suppress ISDN because it doesn't offer them the best returns on their investments. The phone companies also make big profits on expensive, special services, such as Frame Relay. They position ISDN as one of these special services, but ISDN isn't special enough to warrant the high price tag. It's not in the phone companies' best interest to promote ISDN, but it is in the best interest of everyone else. ISDN is the right solution for continuing the technology revolution.