Why'd Everyone's Favorite Airplane fail?
I've always seen the L1011 as a case where the "best" product in terms of engineering and design excellence (including features and performance) fails at the hands of a "mediocre" design. Mediocre in all other ways except for cost, that is (at least in the short term).
Plus the widebody twin revolution came along and put a short end to both the L1011 and the DC-10 before too long.
Add in the political issues and that's about all it takes.
--Nick