There are two motivations. There's what /u/ShittyStartTo2017 said, and there's also the fact that a giant, responsible insurer that's still profitable knows that extreme deregulation the likes of which this bill allows will completely destroy the market.

Assume for a moment that BC/BS tries to keep up its current insurance plan. Then a smaller, shadier insurance company comes into the market offering SUPER LOW, FULL COVERAGE rates.

Idiots switch in droves. BC/BS can't afford its current model anymore and loses short-term profit while it struggles to either keep up by charging people more or by lowering rates to the shady level.

What does the shady company then do when someone gets sick? Raises the rates. By tens, hundreds of times. It fully prices all sick people out of coverage while the oblivious non-sick droves continue paying money for literally nothing.

If BC/BS lowered their rates to keep up, they have to start doing the same thing, or they become unprofitable.

People start to get wise on what insurance companies are doing. The market collapses. Large, established insurance companies sure as hell don't want that.