I was recently fined for parking my vehicle in front of my Avalo

Avalon - I was recently fined for parking my vehicle in front of my Avalon home with a Pennsylvania plate with an expired registration sticker. Pennsylvania stopped issuing the stickers in 2016. The majority of Pennsylvania license plates have expired stickers. The rest have no sticker. Why is Avalon Police ticketing me for this? It seems very unusual. Does Avalon Police not know that the stickers are not used anymore? Is it even possible that the Avalon Police are looking at the thousands of expired and missing stickers and fining owners? I'm at a loss to understand this!