why it didn't sell better: heavier, so dearer trip cost than DC-10; dual-skin hull, so bilge, attracting corrosion; Expat.Brit (ex-TSR.2 &tc) Agency-designers, so brick-dunny (see VC.10 v.707). Some vendors as second-choice and unique (e.g: Ham Standard APU/environmental control, Garrett taking DC-10), so low volume, so slow/dear/losing interest: e.g the up-and-over pax door actuator was by one-off Talley: spares pain. GE (and on DC-10/40, Pratt) exploited the RR(1971) Ltd. confusion: RB211 "doomed".
US' carriers had split 1968, TW/EA launching L.10; AA/UA: DC-10, deferring breakeven for both. Douglas' new paymaster, McDonnell sank good $ after bad, MD-11...and expired into Boeing; Lockheed's new paymaster after C-5 bailout, US taxpayer, after -500 dumped twin/upgrades...merged with Martin and became mighty. Civil design soaks cash; easier to build bits to others' designs; "best", in engineering and feel, may not win at market. See GD: CV.990 - fastest, lostest, v.chunks of DC-10/747 - low-risk, high margin.