Corey doctorow writes about this in his brilliant book "Enshittification - Why everything suddenly got worse and what to do about ut it.".

It's to take away the power for drivers to choose rides based on earnings.

The tipping is manipulated by the company both towards drivers and customers, to optimize for profit above predictable earnings for drivers and reliable service and fast deliveries for customers.

It's algorithmic manipulation and "twiddling with the knobs" to bring in marginally more profit and less payout per transaction.

Just like Uber does with it's transportation services. Drivers that take any ride that comes up, earn less pr drive, while drivers that are reluctant will get incentivised to drive more (and then gradually earn less).

Companies are using the huge amounts of data they have to manipulate both customers and service providers, it's the devil in all these "middleman" businesses. It's a rotten and hugely shitty way of doing things and its gradually becoming the norm for fucking everything.

I cannot recommend Corey's book enough, not only is it clear and concise in describing these mechanisms in several markets and technologies, it's easy to read and witty with Corey's beautiful bitter sarcastic takes all the way through.