The problem is that people just don't buy a lot of tablets compared to smartphones. This is true of iPhones and iPads also. If you take a look at the most recent annual SEC report for Apple [0], you can see that Apple sold 5 iPhones for every iPad in 2017, and the number of iPads sold has dropped for the two years prior to that. It doesn't matter if Google/Nvidia/Samsung could or couldn't make a good Android tablet when people just don't buy many of them, unfortunately.

That said, I still have the Nexus 9 I got at Google I/O 2015, which didn't really live up to expectations despite costing as much as an iPad a the time. The rubberized plastic has begun to wear off, the display has started to show a small air bubble (!) in the top corner, and the flash speed is so slow that you can actually watch Chrome animate a new tab open. Not to mention Android 7.1 is the latest update for that device. I don't think Google tried to make a tablet that people would really want, so a bit of a self-fulfilling prophecy there.

I say this as a full-time Android developer, so maybe my expectations are a bit high, but who knows...

[0] https://www.sec.gov/Archives/edgar/data/320193/0000320193170...