Tipping through the app is much more convenient because I rarely carry cash.
And your point is kinda negated by the fact that Lyft usually pays more than Uber.
Lyft currently pays more, because that's probably last thing that keeps them alive. Many drivers work for both, if Lyft would pay same or less then what would keep them there?
As for the negating point, this is not something that happens instantly, but if you want an example then look at restaurants. There's even special minimum wage (currently $2.13) for jobs that receive tips.
Not in California.
Tipping through an app allows the employer to pay them even less because "they receive tips", in the end you're tipping the company that hired them.
This makes drivers expect to be tipped (even if they did usual or mediocre job) and essentially becomes a hidden fee.