there is some prevention baked into this. someone who wanted to vote as you would have to know that you're registered (or register for you) and also know you weren't going to show up. in PA, in order to register, you need a drivers licence # or SSN. if they don't register for you, they need to know that you won't show up too. if you show up twice, it gets flagged and investigated.
so in order to pull this off they either need your license #/SSN and need you to not try to register yourself or vote too. then for it to matter at all, they would need to do this on a mass scale. that's an extensive operation and with the incessant investigations by republicans, you would think they would have found something by now right?