It is likely due to age and popularity. At this point PCSX2 is the only widely popular emulator you’ve listed, but is older, in the same way Dolphin is old and less of a concern of harming their limelight. That isn’t to say those other emulators aren’t making waves lately, but there is a window between age and popularity that makes this software a prime target. Especially emulators for current gen, which has been historically very rare, and when it did exist were no where near as good as CEMU, Yuzu, and Ryujinx were.
In general I’d agree, although Citra feels like an exception. I’m not quite sure why they targeted that one so hard.
Probably for the same reason Nintendo shuttered the stores for 3DS and Wii U over the last year. They are attempting to consolidate infrastructure, support, user base, and sales.
I think this also shows how underpowered Nintendo consoles are; the Switch is essentially a slightly upgraded Wii U, which itself was only marginally better than the PS3 and Xbox 360! If Nintendo really wanted to combat piracy, all they had to do was beef up their flagship console to the point where it’s hard to emulate.
