in 2015. That was mostly due to poor engine architecture because of Mclaren's resistance to alter their chassis design. They forced them into a configuration that Honda knew would be a problem, but everyone had to keep moving forward and give PR friendly interviews. Every time Alonso would complain about having a F2 engine, Honda had to take it on the chin and not roll Mclaren under the bus. Though they never really set the record straight publically, they were not as quiet about the failures of the Mclaren partnership after they joined RBR and had a winning combo. Honda had already joined Red Bull Racing and was successful before they announced they were leaving F1 again, and that was primarily due to Honda executives not being sure that F1 technology was were they needed to go as an overall auto manufacturer. After a re-think and potential tie-in with Aston Martin, they decided to remain in the sport and I believe AMR was willing to work around the existing/current engine architecture, rather than make Honda do a complete redesign.