The cost of putting a trash bag over a camera that is in your local community is likely to be significantly lower than the cost of whomever installed it having to drive all the way back out there to remove it. You might only have to walk 100-200 feet with a step ladder.
At some point, the cost can be pushed from an economic regime to a logistical one.
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.
Lawyer costs the same per hour either way.
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.
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.