If the police have to send someone around uncovering cameras every few days, then that does send a political message.
Lawyer costs the same per hour either way.
Sounds like someone who's never had to hire a lawyer before. They vary in cost and quality, and there's not a 1:1 correlation between the two. There's also many different areas, eg real estate vs corporate vs labor vs immigration vs criminal.
As far as I can tell, the most likely charges for the garbage bag strategy where I'm located would be a maximum $500 fine, which is too low for most people to even bother with a lawyer.
If they wanted any jail time, they would have to try to frame it as obstruction of justice, which is a stretch and would be difficult to get to stick with a jury.
It's to be a persistent thorn in their side and make the cameras more trouble than they're worth.
There are a lot more of us than them. If 1% of Americans cover up 1 camera every six months and it takes 24 hours to notice and uncover the camera, then there would be approximately 0 functioning cameras at any given time.
Think of it like the sit-ins or bus boycotts during the Civil Rights movement. That wasn't causing real damage, it was just a lot of people being very persistent about causing minor inconveniences. That wasn't the only tactic they used, but it was an important part of the movement's success.