64GB is huge. Many common phones only have 8gb. Inexpensive phones these days have 4GB. Super cheap phones for developing nations may try to sneak in with less. When your phone is full, you generally go to the installed app list, sort by size and kill the biggest thing you can't live without. Eventually you get to the point where you have to delete app A to run app B, and then delete B to run A. If your app is smaller, it'll stay installed longer.
I don't know much about developing markets, but I feel like most phones have for years come in 16, 32, 64, and 128 GB sizes. In any event, I'm not sure someone in a developing country with the absolute cheapest smart phone available is necessarily the kind of user Uber has in mind. I'd be skeptical of the idea that reducing app size is the most revenue-driving thing they could do to their app.
