Switching your phone transmitter off is technically required by FCC regulations:
https://www.ecfr.gov/current/title-47/chapter-I/subchapter-B...Realistically there isn't an issue with leaving a cell phone on and out of airplane mode going purely based on how many people forget or ignore the directions everyday and how infrequently there are problems. But I'll make two points:
The idea that a cell phone transmitter can interfere with an airplane is by no means outrageous. Sure, a modern iPhone/Pixel/whatever has to meet certain emissions and interference standards. And modern airliners are designed with some interference rejection in mind. And ancient airliners from the 70s don't rely on a lot of electronic systems at all. As for airplanes designed in the 90s, well it's not silly to ask whether 200 people with 1W transmitters would interfere with the electronic systems. A properly functioning compliant phone shouldn't, but there's still some risk. Incidents do happen, though they are generally minor. I was on an airplane that had to abort a landing and go-around because they couldn't hear the tower over cellphone interference (voice comms are analog). Obviously no one died, but we were still delayed a bit.
It probably makes sense to relax the rules, but it is incredibly frustrating to see the attitude of "if they don't force me to turn it off it must be OK". The FCC requires you to turn off transmitters to avoid interference. The airline asks you to do so for the same reason. Experts in the field (myself included) are telling you there's a small risk and you should hit the airplane mode button. There's zero benefit to keeping your cellular service active in flight at all. But everyone's seen some article on Facebook (or in this case inverse.com) that says maybe there's a big conspiracy and everyone's lying to them. So they take a risk (albeit an extremely small one) with the lives of 200 other people. For no gain at all.
So do whatever you want, there's nothing I can do about human nature, but believe me when I tell you there's no government conspiracy to make you press the little airplane button funded by the cell phone companies. Yeah, the risk is probably negligible - it's just really hard to prove it and easier to make a small ask of passengers.