The problem in many cases is that it's hard to prove who actually owns the blocks. Who do you fine when you don't know who put them there? They're so cheap to setup that they can easily be replaced if they're removed.
They can as easily fine a business for not removing the blocks as for placing them, and it's not like there's a question about where the blocks actually are.
It's more a matter of how far you're willing to go.
The block has flowers painted on it, it’s pretty. Why can’t I park a block on the public street?