Even if they did, it takes seconds to produce a new account. It is all to easy to produce something that looks like one of the regulars here, with the only difference being the points/level etc. which you only see if you take time to hover over their avatar.
If Yahoo wanted to make this a serious discussion board, and I suspect this is true for many other places in YA, they would need to:
get rid of anon users.
Only allow one Id per user (maybe IP address or MAC address)
Have a real review of reported questions, not just automatically delete them.
A hard ban for people who disrupt things (again MAC address, or IP, or block any account that has the same verified phone or recovery contact)
But it is easier not to do any of that, and so the signal-to-noise ratio here is awful, and 95% of it is trolling or a slagging match.