If they paid those things then (a) the hourly would be significantly less and (b) there'd be less flexibility in hours-per-week or hours-per-month, because benefits are paid at a fixed rate.
> there'd be less flexibility in hours-per-week or hours-per-month, because benefits are paid at a fixed rate.
You're not wrong on point a), but I don't think we'd see a "significant" difference though - but you're incorrect on point b) because I've had (and have) very, very flexible working conditions with the same full benefits as everybody else. Benefits don't necessarily have to be fractional nor tied to any kind of fixed rate. If a company wants to extend its health-plan to its part-time workers there's certainly no US tax-code or insurance reg stopping them - nothing other than the generosity (or lack-of) on the part of company leadership.
I guess in theory you're correct about (b) but the implications for (a) are that the hourly rate is even lower for people who work few hours. A person who worked 1 hour a week would need to pay the company in order to true-up for the benefits.
DoorDash isn't avoiding anything by not paying benefits -- they are paying cash instead of benefits. Maybe it's the case that the employees should net out more than they do; but that's quite separate from whether they get benefits or not, because it's all cash out the door at the end of the day.