Can you force non-pdf generating copy/paste?

In my experience, having "copy PDF to clipboard" is what enables PDF-format copy/paste functionality. If you have that checked in your  Indesign prefs, then Indesign will generate a PDF of whatever Indesign content is in your paste buffer when you switch to another application. That basically takes the same amount of time/processing that it uses to export a PDF file, so if you have a lot of content or very complex content (lots of points/paths) or a very large image as part of the copied material, it can sometimes take a bit of time to take whatever you've last copied and compile that into PDF format ready to paste into AI or PS, etc.

This can be exacerbated if you have a slow drive or are working with linked files over a network. For example, if you have a 300MB PS file placed in Indesign and copy/paste it onto another page in Indesign, that function is nearly instantaneous because it's simply duplicating an instance of that image within the Indesign file—just a bit of code that says "place this image here". But if you switch to Illustrator, Indesign has to download and embed that whole image into a PDF package that it can then dump into whatever application you happen to switch to. If you disable that functionality, then all that's left in your paste buffer when you switch apps is proprietary Indesign code, which gets you a lot of nothing when pasted into other apps because they use an entirely different way of describing content.

It can be super handy when you need it, and annoying when you don't want it, but at least you can toggle it on and off in prefs.

Digression: One interesting thing about PDF format is that it's (pretty much, or at least can be) native Illustrator file format. So when you paste from Indesign into Illustrator, Illustrator "unpackages" the PDF file and you get editable content, even though it's not as tidily built as you'd want (whole lotta nested clipping masks—that's kind of Indesign's thing, having everything in containers). And you've probably noticed that when you paste stuff from Indesign into Photoshop, you get a Smart Object (unless you've opted to paste pixels instead) that then opens in Illustrator, NOT back into Indesign. Why? Because that smart object is a PDF, and AI is CC's PDF "editor." I do dream of being able to set a pref in PS so that placed smart objects from Indesign could round-trip back through Indesign for editing rather than Illustrator... but I'm sure there's a good reason why that feature hasn't been offered.