I think the US market is less impressed by the strange Japanese titles, full priced ports and indies. For Japan these are normal affair, but the US is more about COD, Madden and AAA titles which the Switch is weak on. I just got a Switch and struggle to find five games I would buy. I'm buying games like Minecraft which I already have on four platforms.
No question Switch is respectively more popular in Japan than the US, and you are right, many of the most popular titles in the US such as COD, Assassins Creed and Madden are all absent on Switch. The success it is having is actually made even more impressive by that fact. Switch is outselling the Xbox One on a consistent basis despite not having those titles.
I too am curious why you bought a Switch if the library doesn't impress you. Five titles? Zelda BoTW, Mario Odysey, Splatoon 2, Mario Kart 8 Deluxe, Bayonetta 1+2, Donkey Kong Country TF, Mario Rabbids and a ton of fantastic Indie titles. For me I have enjoyed games like Doom and Wolfenstein 2 on my Switch despite other consoles having superior versions for less money, but I can see how some people couldn't justify the purchase. The bread and butter for Switch is the Nintendo first party lineup, but the Indie library is nothing short of spectacular. I would bet a lot of people play Indie games almost exclusively on Switch. Mighty Gunvolt, Steamworld Heist and Dig, Runner 3, and Shovel Knight to name a few are very high quality.
Late ports at full price are normally doomed, but Skyrim SE has done very well on Switch, and Crash Trilogy is the fastest selling Switch game of the year so far in the UK. Late ports seem to still do relatively well on Switch, and publishers will likely see that as a good thing, and continue to bring legacy software to the platform. The library on Switch is already massive, but if your all about COD and games like Project Octopath are not interesting to you, then perhaps the platform just isn't for you.