If they had to reclass as employees, they would just raise prices to end consumer 10-20% to compensate (or fund it via other's money like they're doing now to price out rest of market).
They'd also put a cap on hours per week so drivers couldn't drive more than 30 hours per week. Companies aren't legally required to give benefits to part-time workers (up to 30 hours).
The big draw of independent contractors is that you've just converted labor from a fixed cost to a variable cost. There are tons of Uber/Lyft drivers (namely, anyone not doing it full-time, which is the majority of drivers) who prefer this since they can drive as much or as little as they want.