I remember watching the hearings in the 1980s when caller-ID was coming to NY state on some UHF channel.
There were two groups of teary-eyed women, one arguing for caller ID (so they'd know the numbers of people calling to harass them!) and one arguing against it (suppose they were in a "safe house" but needed to call their abusive ex- to ask something! They could be identified!) I think the "anonymous" option was to appease both sides. And that's why they can't be blocked.
If only the customers knew of the unpublished GSM setting in the HLR that forces all calls to not be anonymous. :-) I had it when I worked in the cellular industry. Sales companies and scammers despised it. And yes, if you had your own SS7 link, you could spoof caller-id, but that could be fixed with a law by holding telco's accountable for mismanagement of their SS7 signalling network and bumping switches off the network that repeatedly violate policies.
There were two groups of teary-eyed women, one arguing for caller ID (so they'd know the numbers of people calling to harass them!) and one arguing against it (suppose they were in a "safe house" but needed to call their abusive ex- to ask something! They could be identified!) I think the "anonymous" option was to appease both sides. And that's why they can't be blocked.