Uber seems to be in 581 cities [1] while Lyft in 200 [2]. So this is 3x difference.

However, Uber is more global, therefore has much more large cities around the globe. It wouldn't be unreasonable to assume that on average cities are 2-3x larger.

This alone could justify valuation gap. I would also assume that because of global presence, Uber has higher usage due to travellers.

[1] http://uberestimator.com/cities [2] http://www.theverge.com/2017/1/25/14383370/lyft-expansion-ne...