For most transactions in this world, you can't get by without an id number. If you register for a go tournament, pay taxes, use a credit card, etc, you have a number attached to your name. Even relatively anonymous transactions have numbers. If I use cash to buy a burger, the clerk may call out my name when it is ready, but my receipt has a transaction number.
( Note that for the purposes of this discussion I take no position on the sociological contention that such behavior is depersonalizing, nor on the political contention that it is big-brotherish. I simply observe that it is efficient. )
It's not really efficient. A whole stratum of work, investment and resources is necessary to create and maintain a numbering system, and that's assuming agreement (which itself will take a huge amount of time and resources) can be reached. This is massive overkill for a small business like pro go.
From memory, there are only about four cases among current pros where there are pairs having the same name (in English - even fewer in the original languages), and these can also be easily dealt with by the use of Sr. and Jr. or m and f.
Ales Cieply tried to impose a PIN numbering system in his Progor ratings, and he kept it up for a longish time, but he seems to have given up in 2008. The problems he had (and frequently - I know because I had to field most of the questions) were things like an Oriental name being written differently in Japanese, Chinese, Korean, old Japanese, old Chinese or wrongly (Rui Naiwei's name is almost always written wrongly). Whenever he met a name that was new to him, he didn't know if it was a new player or just a spelling he hadn't seen. Often he assumed a new player and made an entry accordingly in the database, only to have to unravel it later once he discovered it was an old player. It's easy to imagine the huge amount of work this takes, and why he eventually grew sick of it.
It would, of course, be possible to give every entry in the GoGoD onomasticon a number, but then there is the question of propagating the system and maintaining it, and all the public would get is a number - to do what with? If you use the onomasticon instead, which works perfectly well with text searches, you get biographical details (often extensive) plus all the variant names recorded. That seems more useful, and so efficient, to me. Having an extra number to go with that would be as useful as a fart in a perfume factory.