Well that's a technicality. There's no reason to base practical realities of Jan 1 2020 being the start of the "2020s" with the fact that Year 0 was missing.
> Those technicalities, however, don't change the fact that as a society, we seem to have collectively determined that decades begin in years ending in zero and end on years ending in nine.
It's not even a technicality, really. A decade is any span of ten years, and in modern English we refer to decades by their tens digit. If someone wanted to talk about the 202nd decade or something, then sure, that'd end next year, but instead we merely talk about the 60s, 90s, or whatever. Calendar shifts in the interim even make the "technical" approach a bit of a farce, though.
While millennia and centuries are numbered ordinally (e.g. the 18th century or 2nd millennium), in modern speech decades are not numbered ordinally, they're declared based upon the tens digit (e.g. 60s, 80s, or 90s), so your point is false.
I recall a CNN article recently about this: https://www.cnn.com/2019/12/21/us/when-does-the-decade-end-b...
> Those technicalities, however, don't change the fact that as a society, we seem to have collectively determined that decades begin in years ending in zero and end on years ending in nine.