In the case of losses where people die, it can actually a bit embarrassing for airlines to report a windfall profit while the victims wait years for the minimum possible payout the insurer can get away with. The MH370 victims' families will probably get far less (in total) than the airline was paid within three days of its disappearance—and they'll likely wait the best part of a decade to find out.
Even so, I don't think any airlines set out to have accidents for insurance purposes, but I'd be happy to hear stories from pilots who've been asked to write off an airframe. How does that conversation go...?