Here are my thoughts on why:
Because Wu is a better more skilled player than Souquet ever was.
Because this poll is called "Greatest of All Time", not "Greatest of All Time for Their Era". If it was "Greatest of All Time for Their Era" then you would have a solid point, but that's not this poll.
What I can't fathom is how anybody could rank somebody higher than somebody else who would beat them. Again, this is "Greatest of All Time", not "Greatest of All Time for Their Era".
"Greatest of All Time" means their skill level in their prime compared to somebody else's skill in their prime, meaning if you were God and could transport (and resurrect if necessary) say Luther Lassiter and Mike Sigel in their primes and have them play a race to 30 of 9 ball every day for a month, who would win?
"Greatest of All Time" pretty much requires that a player's sheer skill level/ability on its own, without any regard for how it compared to their contemporaries, has to by far and away carry the most weight. For the most part any other factors such as titles, longevity, consistency, domination over their contemporaries, and the strength and the depth of the fields they faced etc are only useful as tie breakers when two people's sheer skill/ability levels are a toss up.
As Maniac points out in post #76 (
https://forums.azbilliards.com/showpost.php?p=6416469&postcount=76), the only thing that makes this difficult (impossible really) is comparing those who were only good in one or two games against those who were good in many. How do you compare say the guy who dominates in just one or two similar games but isn't real near the top in any other game, against the guy who excels and is near the top in a large number of very different games but wasn't quite as dominant in any one of them?
If this was greatest 9/10 ball player of all time then really only two names are even in the discussion the way I see it. One is consistently slightly more skilled per how he performs in general, and per FargoRate, and per their match ups against each other, and has a great resume but still not nearly as good as the other guy's (probably mostly or solely simply because he doesn't compete in most events though). That would be Wu Chia-ching. The other is almost equally as skilled but has a bigger and indeed pretty massive resume including back to back to back victories in majors with some of the strongest, deepest fields in history. That would be Shane Van Boening. The two are close enough in skill level that the massive resume has to put Shane over the top and get my nod as the greatest 9/10 ball player of all time, but had Wu played just as many events things could have easily been different.
For greatest all around player of all time, aside from the most popular games of 9 and 10 ball, you also have to include all the other games for which there are at least occasional professional level tournaments or some popularity in gambling match ups. In order of popularity, on top of 9 ball and 10 ball you would then also have to take into consideration one pocket, eight ball, and straight pool (and possibly banks although this one is debatable at best). For greatest all around player I would argue that the popularity of the game should roughly correspond to how much credit/weight is given for their ability in it. For greatest all around player of all time probably only Efren Reyes, Alex Pagulayan, Dennis Orcullo, Jose Parica, Mike Sigel, and Nick Varner are even in the conversation. This one is pretty tight but I would probably have to give the nod to Efren when considering who would win the all around match up in their primes, and his resume makes the what was close to a tie (with Dennis and Alex) a little more of a clear cut decision so Efren it is.
Because of the difficulty (impossibility) in comparing those who specialized in one or two games against those who played a large number of games very well, I am still undecided and giving thought to where my points should go.