50% participation rate for a $15,000+ per year opportunity without lifting a finger is too high?
Of course it's way too high.
* Some large percentage of all Teslas, say roughly half, are sold in places where Tesla Network won't even work (like mine!).
* A large number of existing owners, say roughly half, have already stated that they will never lend their car out to strangers.
Multiply this, you'd get more like a 25% participation rate.
This isn't actually the big problem with your estimate.
Much more importantly, you've grossly overestimated the total *demand* for taxi trips, which appears to be the primary source of your bogus numbers. Your original assumptions imply over 600 million trips per day -- basically literally everyone in the US every single day. Which is just not happening for a network restricted to a short list of metropolises, and probably not for a network covering the whole US. Have you ever looked at patterns of travel demand? Obviously not.
And you can't use Tesla Network for any significant number of peak hour commutes. In order to do so, you'd have to have someone who owns a car and does NOT have a peak hour commute -- think about how uncommon those people are. (On top of that, someone who doesn't have a peak hour commute and owns a car is likely to be more protective of it and less willing to let strangers drive it.) So exclude peak hour commutes from your calculations.
This is a case where it's quite possible to hit the demand limits. Assume that Tesla takes 100% of the addressable market, but be realistic about the addressable market.
It is boring trying to explain Transportation Economics 101 stuff to you. Please go read a book on the statistics of transportation demand.
If anyone else is curious about realistic potential, I'd be happy to discuss it with them.