I've always read that the L1011s lack of sales was down to delays with the RB211, and that no long range variant was offered at launch? Douglas did offer a longer range product with the DC-10-30, and the rest is history as they say...
There was also the fact that the DC-10 longer range variants had a centre gear reducing the pavement loading (the L1011-500 pavement loads can be quite prohibitive) and that the design was much more technologically simple reducing costs.