Like, I can really imagine the reaction of professional car thieves when they heard of this new ban: "Damn, Bobby, let's pack it in! I guess we're not allowed to use those jammers any more. Too bad, they served us well."
The other idea is that if the tools themselves are illegal it's a higher barrier to entry for the people who want to get into that kind of crime so maybe some of them will never start in the first place.
And it does work in some circumstances.
They perhaps could have gone with clarifying or strengthening existing legislation instead of course. There's already an offence of "going equipped to steal", but it is hard to prove because you might be able to get a court to believe that you were carrying a bunch of housebreaking tools around in the middle of the night for some legitimate reason.
So that's why we tend to pass laws to target tools.
And yes, hardened car thieves probably won't be deterred, but it will be easier to prosecute them if they're found in suspicious circumstances and found with these now-illegal devices. It's not like criminals usually think they're going to get caught - the deterrent effect simply doesn't work on some people.
First, a “throw the book at them” approach leads to easier convictions via plea deals and the ability to be guilty of one charge even if another doesn’t stick.
Second, if lawmakers did not adapt the criminal code in the face of new technology then we’d all be posting here about how out of touch and behind the times they are. Or we’d be bemoaning how law enforcement can’t go after this type of crime because it turns out not to be explicitly illegal to maliciously block RF signals used to lock doors.
And also, writing new policy is their job? Are you just suggesting that we pay lawmakers to never try to address things affecting their constituents, because we care about what the criminals think?
Will the new law lead to more car thieves getting caught? If not, it's just a symbolic gesture to the electorate: "We know you want us to do something about car theft; this is something."