Both companies knew that there was only enough market for one double decker. Since the airline market had experienced clashes of sizing before (if I recall correctly, the MD-10 and TriStar overlapped too much and so neither became a big money maker).
Quite a bit off the mark, while many loved the L1011 it never performed as well as the DC-10 especially with production of the -30 and beyond. The best production numbers I can find are 386 commercial DC10's with an additional 60 military KC10's and if you will the evolution of the MD-11 adds another 200 craft for a total of approx 650 aircraft. There were approx 250 L1011 produced. The MD-11 and converted MD-10's are still being flown with plans for replacement by the US based FedEx cargo company (hundreds still flying), you may find a few L1011's operating.