The law is the law. Why should it be changed to levy tax at the time of purchase?
Oh let me guess, because the institutionally corrupt government of California is pissing away too much money so they're trying to wring every last dime out of everyone in the state in the most efficient way possible?
Oh change the laws, throw the bums out? Unfortunately most Californians are too stupid to realize that the democrats have gerrymandered themselves into permanent strongholds that are all but impossible to root out. Hence we are stuck with the bums.
The legislature needs to figure out how to live within their means. Cut everything until outflows met inflows.