They're different communities, with different standards.

I took a Lyft recently from a driver who had an excellent rating. He happened to also be an UberX driver and confessed he had almost been kicked out of Uber because he was getting bad ratings. All his feedback was along the lines of "driver is too chatty, tries to make unnecessary conversation". With Lyft, the whole point is that your driver is friendly and makes conversation.

Uber drivers seem to be strongly encouraged to offer water and gum where only the occasional Lyft will have either.

There are a couple other small differences but yes, drivers and passengers select which community they want to be a part of. Depending on which aspects of each you prefer, the qualities definitely differ.

I have no clue; I've never used them or been involved with them. I'm simply pointing out that comparison on cost without even the attempt to analyze quality is a recurring theme that encourages lower prices without consideration of any other factors.

They obviously have all sorts of quality metrics. What exactly do you mean? Driver density, time to pick up, time to deliver, routes taken, feedback ratings, car quality, etc.

Sure, but none of those metrics are dependent on the particular service in any real way. They're either a) properties of an individual car+driver or b) properties of the city/traffic situation/environment in which that driver operates.