They were trying to get new airliners to market basically until the merger. Their problem was that they had gambled on the future of the passenger-carrying trijet when it was obvious that large twinjets would be the way forward (except for the odd high-capacity or long-range quad). Their five-abreast cabin in their endless line of DC-9 derivatives was also seen as antiquated and limiting. Boeing was doing pretty well though, competing with Airbus, which made them attractive for a merger.
By contrast, McD’s military contracts were pretty healthy, and they continued manufacturing variants of the AH-64 Apache, AV-8B Harrier II, C-17 Globemaster III, F-15 Eagle, F/A-18 Super Hornet, and T-45 Goshawk all the way through the merger. Boeing’s military side was weaker and they wanted a slice of that.