Pushing an industry into self-regulation has long been a way governments use to reduce regulatory burden and inflexibility to change. Letting them know they had better solve a problem or the government will solve it for them, probably in a way that's worse for everyone, can push industries into action. Sometimes it works, sometimes it does not.
It also helps raise public awareness of the issue. Most people have no idea how much info automakers are sucking up about consumers. All the “connected” infotainment systems in modern vehicles can phone home whenever and with whatever data they want, and it’s all implicitly allowed by arcane provisions buried in the terms of service.
The digital surveillance apparatus, of which this car business is only a small corner, spans industries and sectors and is valued at many tens of billions of dollars per year. There's no chance that a senator sending a letter makes more than a tiny and transient blip. There's a reason we have an EPA and not just the occasional sternly worded letter about too-flammable rivers.
they prefer to give industries the opportunity to increase their political donations and let the issue slide rather than take action to fix it.