Agree that the lock-in is weak compared to other markets. Their strategy has been to incentivize drivers and riders to not split usage between other apps.
Uber drivers who do a certain number of hours or rides per day/week often get bonuses, so they'd have to forego these bonuses to split time with Lyft.
On the rider side, they're pulling a play from the airline playbook, with their version of frequent flier miles and status: https://techcrunch.com/2018/11/14/uber-rewards/