Also, it might be a different company, I imagine competition is fierce.
It would take quite a while to save up for a plane ticket, and they would be risking their job if they abused their access to the phone system. If they somehow do own that scam business, then anything they do risks their profit margin.
The foolishness of such moves is why they are newsworthy and many things must fail to make then happen. Perhaps this is why the wikipedia list[1] of them numbers 15 and many several federal charges against the person. These are all crimes that open up that business to risk and legal repercussion. The last thing a scam business wants is an international incident drawing attention to them. I almost welcome if it means the long term shutdown of those parasites.
These don't appear as "anonymous calls from India". Just like the spam calls, the caller IDs are spoofed to appear local.
It has zero effectiveness if someone decides to send a hundred thousand spoofed VoIP calls at you because you lost them their spammer/malware job by stringing them along.