they allow spoofing of numbers and they have a phone system that doesn't let one side of the call hang up (in the UK). If the Telcos were made responsible for all losses (including consequential) then they'd close these two holes so fucking fast it would make your eyes bleed.
Both of those exist for a reason.
Remember that Caller ID is a presentation service, it is designed to allow the caller to present a number of their choice to the called party. That is often a switchboard number, or an 800 number, so there may be a good reason that it isn't the caller's actual number, and the telcos are unlikely to remove that functionality. The network still has the "real" number available, for billing purposes, and with suitable permissions (police warrant, 999 operator, etc.) it can be obtained. This obviously only applies for calls within the same network, no telco has control over signalling information sent from another network, they have little choice but to believe it. That's why these scammers work from international locations like India.
As for the ability to terminate the call by the recipient ("called party clear"), the original mechanical telephone network design had to choose which end would control the call, since there was no separate signalling network to send a cleardown signal to the other end. Logically the caller, who is paying for the call, was given control. People got used to that, you could answer a call on one phone, then hang up & pick up an extension to continue it in another room. With the advent of electronic exchanges and SS7 signalling it was no longer mandatory, but until recently there was no good reason to break a functionality which had been useful for decades, so even when the called party hung up the line would remain open for 2-3 minutes. The growth of scam calls changed that, and about 10 years ago BT changed the system so that by default a call will clear 10 seconds after the called party hangs up, and they are considering reducing that period. Again, once you cross networks (more common now that there's no monopoly supplier) things get complicated, since you're relying on the caller's network correctly handling the signaling message.
At the end of the day the best approach is common sense. Does what the caller is asking you to do make sense? If not, don't do it.