Idk it just doesn't send the right message.

I don't think the activists are really worried about messaging. The political system in this country has completely abandoned these people and left them no choice but to take community defense into their own hands. Both political parties have doubled down on border fascism, building a bigger police surveillance state, building more prisons, and building more police counterinsurgency training centers. These people aren't out here trying to convince people to vote for Democrats. They are taking direct action to inhibit raids in their community.

Why not smash actual ICE cars?

They did on a few occasions. The majority were LAPD because they formed the majority of the repressive forces deployed so far.

It is worth noting that Waymo is a Google property though. Google is a significant defense and surveillance contractor that provides technology to ICE.