Inbound SPAM Mail Not Caught

Why can't Verizon stop incoming SPAM the same way they stop me from sending SPAM they let through in the first place? Anytime I try to send the FCC a copy of the SPAM mail Verizon allows to reach my account, Verizon identifies it as SPAM and prevents it from being sent. If Verizon can identify the mail as SPAM on the outbound server, why can't Verizon identify it as SPAM on the inbound server? Also, sending anything to the is a futile effort because it seems that nobody is reacting to these e-mails. For months I have tried to bring this to the attention of Verizon via chat, the phone and snail mail without any result.