I wonder why the tablet app ecosystem on Android is so poor? Could it be that the Google has spent the best part of the last decade firmly pretending that Android tablets don't exist, and people should just buy a Chromebook? Maybe that might have something to do with it?
I agree with the first statement and firmly disagree with the second. Chromebooks are not inherently tablets and they inherently do allow multiple windows open at once without split screen, something that you basically never see with the tablet computing paradigm.
Finally. This is my favorite side effect of the advent of foldables - more people seeing the big tablet landscape mode of apps, and thus the fact that so many apps are incompatible coming to light.
I wouldn't be surprised if the unsaid part is that they're focused more on productivity apps than social apps, but I could be wrong. Also wouldn't be surprised if Instagram doesn't care about getting downranked, given its brand and market awareness somewhat transcends the need to appear in top-apps lists.
What carrot? A carrot is an incentive. Google didn't embrace the tablet format until very recently, in the grand scheme of things. They haven't offered devs any special deals that I'm aware of — say a revenue split from the play store or paying them to deliver a tablet version of their app — so they didn't incentivise devs to focus on Android tablets.
iPads have dominated the market for so long, and remain a fairly predictable and consistent device to develop for, so... why would an app developer have poured time into an app for Android tablets in years past?