in 2008 uft-8 was only ~20% of all web pages! Again, that deprecation fact is not meaningful, a quick search shows that rfc for tagging is dated 1999, so that's just 10 years before deprecation, that's a tiny timeframe for such things, so I agree, it's not surprising there was no widespread use.

Out-of-band metadata has plenty of other problems besides the fact that it doesn't exist in a lot of cases