The way I see it is you have a choice, put the ugly stickers on and drive in the carpool lane, or don't put the ugly stickers on and don't drive in the carpool lane. There are instructions to where the stickers are supposed to be placed and they are made, like your registration to be permanent until they expire or you don't want to use them anymore and remove them.To me the reason to not put the stickers on is they are ugly. California should come up with a smaller decal that could fit on the license plates or something similar. Since I rarely need to use the carpool lane, my thinking is to simply attach them with tape to the windows of my car when I am on a trip that I expect to need to use the carpool lane. Technically CHP could pull me over since they are not in the right location, but I think they would have higher priorities than that. Just like I notice many cars, including many Teslas, driving around without a front license plate.
There's a big difference between a $500 carpool violation ticket and a $25 front plate fix-it ticket. So the incentive for the CHP to enforce carpool violations is obviously greater from a revenue standpoint. But, HOV lanes have Federal mandates for minimum speeds that must be maintained. If the State doesn't meet the minimum requirements they can lose Federal funding. So there's millions of dollars at risk giving CA incentive to enforce carpool rules vs your lack of a front plate.