Keeping backward-compatibility requires people that care. That have enough pride in their work to counter-balance the grind.
This is true for most people working for large multinational corporations. Good things can still be developed without passion.
There's nothing wrong with that, and when I'm at work, I do my best to do a good job and make reliable, maintainable systems. Those two things aren't in conflict.
It might not be a good business decision for Google, but surely if they create enough positions that are solely focussed on the boring stuff but are paid better to make up for it, there is a price point at which they'd get enough interested people.
MS pay is actually competitive for external hires, although internal raises aren't usually very high.