Not the whole truth.
If you mean that they sell everything they can make, like before it hits the stores globally, that is only true for PS5, never heard anybody seeing them on stores yet.
Series S have been available since the launch on many countries, and series x have also been seen on stores around the world (not USA I guess) rarely. I saw 3-4 units on few different cities few weeks or months after the launch.
Series X have been now available on some stores on some countries, like here at Finland Series x became avaiable few days before xmas on the biggest electronic chain, and have been available since on majority of their stores. So, it didnt sell out even just before xmas.
That is how I got mine, just walked in and asked to get one. So, they have been available for 3 weeks now, and they eventually will sell them, but demand seems to be lower than supply now. (here)
And I dont mean not by all means that series consoles arent selling better than xbone, but just pointing out that it is not factually true that they sell everything they make, if that means that they would be sold out globally.
But compared to gens before, yes this is weird situation as it is the first time I remember since 80's that any console is sold out for more than 1-2 months (PS5) and that even xbox have been difficult to get (XSX), because traditionally only playstations sell out here.
I have never bought xbox as new, had OG+360 used but didnt play much.
So xbox have done things better than before, as I would not have even considered to get one before.
And the first time I feel like they are like brothers that can fulfill each other, instead of being like in the movie Twins where one brother is small and weak, and one have every interesting feature
Not everyone live in US/canada, and yes, series S have been widerly available on many EU countries at least + also on (10-15%) discount.
And I dont mean that "I saw one here and then", I mean "walk into a store and buy them almost any day of the week". Now Series S isnt that easy to find vs. before xmas. But both systems s/x are still available on big part of the country.
Yes, USA is the main market, but it gets old when some people talk like there isn't hundreds of countries.