Eh ... you know that the majority of the world's population lives in East and Central Asia? And that their office hours are (roughly) between 0 and 14 UTC? Granted, not all of them speak English, but there's a world outside the US and EMEA.
Also, that graph is from 2009. The world has changed a lot since then (even before the pandemic), and so has Stack Exchange. This is the current situation (top line); most questions are asked between 9 and 18 UTC.
It's not much different from my research from a few years ago.
I can't help but notice that it's definitely not the bounty rule causing your question to have no answers yet, it's your impatience (sorry for being so blunt). That question is not even an hour old right now; we're volunteers and nobody is forced to answer your question. If you're in a hurry, Stack Exchange is not the place to go; what we aim to do is to write good, comprehensive answers, and that takes time.
OK, this is interesting. (Or my SEDE skills fail me; it's late night here already.) I've grouped Stack Overflow questions by posting hour and checked which % of them received an answer within x hours. That produces the following graph:
If you want a quick answer, you have a slightly higher chance of getting a quick answer between 6 UTC and 22 UTC (the bottom line); at the same time, those hours have the lowest percentages for being answered after 24 hours (the top line). I have no idea how to interpret this ...
If you're looking for absolute numbers instead, like the graph in your question, check the top line of this SEDE query.