It's not like Wario's car and bike were in Mario Kart.Given how anxious Mario games always are to acknowledge the Yoshi’s Island and DKC series, I never understood why Wario games are the exception. It’s not even because they aren’t platformers, since Wario platformers absolutely do exist and don’t get acknowledged either. Not even in Smash.
Those are just a few select examples, I could also bring up the Amiibo Party board in Mario Party 10, Wario's (and Ashley's) mystery suit in Mario Maker or the Shoulder Charge from Mario Golf World Tour, did you know about that one:I’ll be honest, I only knew about those first two things. That Super Mario Party one is the biggest shocker you’ve listed, that’s rad.
The vast majority of those are either extremely minor cameos or over 10 years ago though. The Wario Bike isn’t in Mario Kart 8, for example; why cut that?
Even still, none of those would be as significant an acknowledgement as a fully playable character from those games. Heck, I wouldn’t “just add Ashley and call it a day,” I’d add a Diamond City track that has actual references in it unlike the MKGP track, add lots more Wario music to Smash, and so on. Heck, a “Hurry Up Bomb” Cup sounds rad.