When they launched, they made an Instant Pots, and it was a fairly good product, with good marketing. There were other pressure cookers before, but this was beyond easy to use -- and super Instagram and Facebook friendly to share cooking videos.
But then they expanded out to... Air Fryers, Coffee Makers, even Air Purifiers... and it's just too much. They weren't going up against old pressure cookers that hadn't really been updated in 40 years, they were going up against established modern brands like Nestle and Keurig, and whoever else.
And they never really established a reason for all the different devices to live under that brand... and probably lost quality control (as you said). And yeah, I mean... I got an Instant Pots as a housewarming gift in 2010, and I loved it. So I gave Instant Pots to a bunch of friends as housewarming gifts... and it never seemed like a hit with the people who received it. At one point someone told me, "Thanks, but I already have one..." So I figured I'd replace my old one, and holy hell the quality in like 2017 or so was not good.
Like you pointed out the measurements on the sides were not accurate. And every dish I had made in the old Instant Pot didn't cook right in the new one. (Probably because the temps were off.) I was an idiot and tossed the old Instant Pot I had before really trying the new one out... then when the new one sucked I stopped using it all together and never bought another one.
Edit... here's a pressure cooker from like 2004. It was such a pain to clean and no matter what I did it splattered steam and liquid all over when it was turned on. Instant Pot was so much easier to use than this thing was.
https://www.overstock.com/Home-Garden/Wolfgang-Puck-7.5-qt.-...