It hasn't even been 6 months since the system launched. It launched March instead of November, so no Holiday boost for Switch (Black Friday, the entire month of December). And it's hard to sell software when there isn't any hardware available (didn't stop Breath of the Wild from outselling the Switch itself during its first month, but I digress). Which is the main reason pre-orders for Splatoon 2 (currently unavailable on Amazon US by the way) aren't as high as they could be, because nobody can find the system it's available on.
Hardware Comparison Threads:
Current Thread
Is Hardware Getting TOO Powerful?
Older Threads:
PlayStation/Xbox/Switch: 2022 Edition
PlayStation/Xbox/Switch Hardware Battle: 2021 Edition!
PlayStation 4/Xbox One/Nintendo Switch: 2019 vs. 2020
PlayStation 4/Xbox One/Nintendo Switch: 2018 vs. 2019
PlayStation 4/Xbox One/Nintendo Switch: 2017 vs. 2018
PlayStation 4: 2015 vs. 2016 vs. 2017