The WiiU is an older, mostly dead platform, with a replacement on the market in the Switch. The Playstation Classic, even flopping like it did, is new and people want to see what they can make run on it.
And man, some of you guys are unreal. Literally in here throwing tantrums because a dev isn't doing the free work you want them to. If you're bothered by the lack of PPSSPP on WiiU there are options. Wait, make it yourself, buy a platform that has PPSSPP actively developed for it, or (and this one might sound crazy) buy a PSP.