There were several things that hobbled L-1011 sale. The first was the decision to limit engine choices to one manufacturer. It was physically the smallest of the three big fan engines and when Rolls stumbled they couldn't fit either of the other engines without major structural redesign. The DC-10 offered both Pratt and GE and could have fitted the Rolls as well.
Lockheed made no provisions in the basic design for a high gross weight version while the DC-10 design left room for the third MLG to reduce footprint pressure. Their idea to add a wheel to the outboard side of each axle would have required a huge bulge in the MLG doors.
No factory built freighter or Combi versions were offered. In the end, there were only seven converted to freighters for commercial customers even though there were fleets of surplus pax versions available. That says something as well.
LCC's absence from the commercial market after the L-188 didn't help either as they only had one product to offer.