As usual, the reality of the financial situation is fairly complicated. Doordash guarantees minimums that other such services do not. In other words, in many ways, Doordash was more friendly to their 'contractors' than other services.
If they had simply chosen not to be unethical and lie to customers about where their tips go, they could have had it both ways.
... it's just that they reduce _their_ fee paid to them by, coincidentally, the same amount.
And claim that this offers the Dasher "stability".