TA actually had plenty of success during it's times. It got a few game of the year's, had a hell of an expansion pack, and gave Chris Taylor quite the reputation. It sure as hell blew Dark Reign away.
Starcraft was released quite a bit after TA, so they didn't really compete hardcore.
Pretty easy to understand why cavedog is no more, however. The main man Taylor left, and Kingdoms was more than enough to slay, or at least shame, the mightiest of companies.