You're saying basically that investing money in developing your product to gain more customers is a waste. You're also saying it somehow makes more sense to develop two different applications for two different platforms and depend on a THIRD service's platform (Facebook).
Instead of just making one simple web 1.0 mobile site that works everywhere, doesn't limit your customer base, and takes less time and money to develop.
And it's not nonsense. I'll bet you that some basic research on demographics of the user base would show a clear separation in the economic disparity of cab users vs lyft users.
Why the separation? Easier access to cabs. Poor people will find it more difficult to access the internet or a smartphone, but they can get easy access to a plain-old telephone or desktop internet access.
The assumption is based on socioeconomic class differences, and is perceived rather than actually noticeable in difference, but i'm not going to repeat what you can find on wikipedia. The other aspect is that rich people may be perceived to tip better.