' 75 ... and poncho took a bullet in the tongue...
1. Lazenby only did one film as he was given bad advice by his PR people (they told him that Bond was a 60s thing, and that the approaching 70s would drop the series like a sack of hot shit). Plus there was the fact that OHMSS, despite being quite successful at the box office, made a lot less than Connery's last few films.
2. At the end of OHMSS Lazenby portrays Bond at his most unhappy... his wife has been murdered in cold blood by his arch nemesis and his german aide... this profound unhappiness is contrasted starkly with the romanticism and love that came before it, and thus the latter is necessary..
3. Had Lazenby ignored his PR team and done Diamonds are forever, and had Telly Savalas agreed to return, it could have been an excellent culmination of the whole affair... in DAF, Connery is overweight and openly bored with the role... Grey is a rubbish Blofeld... with Lazenby and Savalas in place, the viewer would be reminded of the scenes in OHMSS and it would have undoubtedly lifted both films.