Maps was a cover story. Forstall was fired because he was Tim Cook's only serious rival for power post-Jobs, and also because some other execs (such as Jony Ive) didn't like him. When Steve Jobs died, Forstall lost his only protector in the company.
Spinning up a maps service from scratch to match Google Maps was a monumental task, nearly impossible to do quickly and well. Apple Maps continued to suck for years after Forstall was fired. Not to mention that Siri continues to suck today. Forstall wasn't fired for incompetence. He was a proven executive who was in charge of developing iOS!
In contrast, Hair Force One has overseen a massive downgrade in Apple software design and quality. But he gets along well with the other execs, doesn't rock any boats.