Caller ID was developed in the 1980s and can be easily spoofed because there is zero verification built into the protocol.

In the 1980s, all calls were completed via large, well-known telephone companies, so there was no concern about spoofing.

Later, it became possible to essentially set up your own little phone company and complete the call yourself -- especially with VOIP -- and suddenly the caller ID data wasn't trustworthy anymore. If you set up your own VOIP operation, you can choose what to send for caller ID.

Unfortunately, changing this would be a massive undertaking at this point, as it will break all of these smaller systems attempting to complete calls.

Believe it or not, Caller ID is provided by the calling phone company, not the receiver, and it's send as a 1200 baud signal (lol) between the first and second ring. Most cell providers will ignore the "first ring" and not actually complete the call being received until the caller ID signal comes through. But on many home phones, you still won't see caller ID until the second ring starts.

There is no verification to the data being sent. The receiving phone basically asks the calling phone, "Hey, what's your number?", and that's what is displayed.

Oh, and have you seen your phone say "unknown" sometimes instead of "private" when the caller ID is blocked? Unknown doesn't mean it's blocked -- it just means that nothing was sent. Private means that something was sent, but with a little flag saying, "Please don't display me."

This is important because when you think you're blocking your caller ID, you're really not. Some receiving phone systems choose to ignore that "don't display" flag, and your number gets displayed anyway.

In fact, I have that going on with my phone. If you call me with a private number, I can see it anyway.

Back in the '90s, they introduced a feature where you had to show your caller ID to get through. However, you could get around it by calling with an unknown number, as it would only blocked numbers marked private. I found that feature to be obnoxious, so I always just called unknown (there were ways to do this) and pushed right through it.

But yeah, all of this allow robocallers to break the law and get away with it. Plus many of them aren't even based in the US, so they LOL at FTC fines.