I care about safe, convenient, and efficient/economical in personal transportation. All other things being equal, sure I'd like for "happy" to be part of it, but not at the expense of the first 3 measures.
A rudimentary search or two would seem to indicate that driver happiness and driver safety are connected. I don't know how to effectively measure it, but it would seem to me that at least some consideration should be paid to driver happiness as a safety factor.
Implying that Lyft doesn't accomplish those?
Not at all. Just implying that "driver happiness" itself is below the fold for me.
I think it's important to recognize that driver happiness is a major component in ensuring the 3 things you do care about in the long term.