Same reason as homebrew died with the Wii, DS and PSP from where I sit. That being where the Wii, DS and PSP (and xbox and GBA before them) represented if not best in class devices then often the only way to do your own code on the move.
Today cheap laptops, raspberry pis (not the first mini computer thing running Linux but compared to the pogoplug/sheevaplug then night and day difference), android and ios phones/tablets that anybody can develop for (using nice languages and libraries, and possibly get paid), TVs with HDMI as standard and HDMI out available on most laptops (and once tablets/phones but it seems that vanished with headphone jacks and SD card slots).
This means any device to get homebrew worth paying attention to will have to have abilities to make it worth it; processing power in a form factor, fancy feature that devs can't help but want to play with, some kind of serious openness, serious library that can't be ported/emulated/adapted elsewhere that means convenience is a thing sought.
Scene in general being up its own arse, devs not playing nice, people having feelings hurt... happened day in and day out for years on everything else and all over the internet for decades before that. While some might say everybody is apparently now all fragile and concerned with feelings, and I will at least note a minor shift towards that as some younger types come in and try their hand which more commonly have such troubles (or at least were not weeded out before then by the crucible that is IRC back in the efnet days), that is at best a red herring of a discussion. I don't doubt someone was all you failed to worship me and deal with my demands so I am going home but as a deciding factor... pah. Kung flu acting as a barrier? Maybe some but not enough to note, unless there really are that few an amount of devs that random chance means enough were or they all got siphoned off to do those juicy remote work jobs that popped up.
That and the Switch is not exactly having a popping game library that ROM hacking types can't help but want to play with. I am actually somewhat impressed it has the cheat making following it does.
To that end you will get a few intellectually curious people that try their hand to say they did, and the Switch has enough power that you don't even need to optimise things as hard as emulators on the DS or PSP so minimal effort/skill gives you a baseline quite playable quality. Sufficient numbers however are unlikely to stick around to make it something to follow like you might have for the GBA, DS, xbox, PSP, Wii.