Sony isn't moneyhatting games that target the Japanese market. They want to focus on the west. More and more Japanese devs have given in over the last few years and started supporting the Switch. The only ones that are never going to do so are Falcom and Bandai Namco Studios, because of Harada. None of his games come to the Switch.

You're thinking assumes that devs can make a game in a really short amount of time.  In reality, most Japanese games take about 3-4 years time to develop.  The third party games that are being released this year are based on how people thought the Switch would sell in 2017-2018 (i.e. decently well, but not super amazing).  Based on that alone Switch is getting a multiplatform version of most Japanese titles.  We haven't seen yet seen how devs have responded to Switch's 2020 sales.  PS5 in 2023-2024 will be lucky to get any third party exclusives that target Japan. 

Game makers like to make a profit on their games.  Switch is selling like the DS, but it's capable of playing big budget titles like a home console.  At this point every Japanese game developer is going to want to put their games on the Switch.  It has everything they want.  At the same time, Sony has mostly given up on Japan.  They aren't going to moneyhat a game from a series that has mostly just sold to Japan in the past.

What you're saying is very sensible and logical, but we've seen that third parties often do not have sensibly or logically when it comes to what systems they support, they often show bias.

PS4 didn't set Japan on fire sales wise yet it was showered with big Japanese games, I see no reason why PS5 will be any different when it is selling faster than the PS4 in Japan.