It's not just safety, it's that the 737 is the symbol of an industry which is not keeping up with the times. The 737 is a 1967 aircraft that is still flying. You don't see a 1967 car being sold in car dealerships. You can't buy a 1967 computer.
You see the headline "Airliners can't take off in Arizona because it's too hot" but the truth is "737s can't take off in Arizona because it's too hot" (737 struggles to take off under good conditions, it takes more runway to take off than planes with 2x the PAX) People say "flying sucks", but it's more like "flying sucks in a 737" (the reason why your neck locks up just thinking about sitting in a window seat on a 737 is because the 737 has a circular cross section that doesn't fit the human body; a plane smaller than a 737 with a more appropriate cross section feels like riding in a 747)
The Embraer E2-Jet is a smaller aircraft that has a bigger engine with better fuel economy because it's not an obsolete design that can't fit a bigger engine. Then there's the A220, bought by Airbus, that Boeing has no answer to and has chosen to have no answer to. For some reason they got possessed to develop several widebody airliners in a row but when it comes to overhauling the narrowbody planes that are most of the units, most of the flights and most of the social and economic impact of aviation, management has been on strike for decades.
The industry has been trying hard to keep you from riding in a modern narrowbody or regional jet because if they did, you'd be demanding it. Once you try the A220 there is no way you'd ride the same route on a 737 if you had a choice. And the thing is the A220 has lower operating costs... But remember, capitalists pay capital costs but they can make you pay operating costs. So long as everybody is flying inferior aircraft they can refuse to invest and pass higher operating costs on to you.