Most planes are full these days. The airlines figured out how to make money.
It’s been many years since I have not been on a completely full Alaska Air 737 to and from Anchorage. My sister works for Alaska and I keep telling her to suggest that they upgrade to 767s so they wouldn’t have to pack us in like sardines. Southwest is the same way.
I remember in the early 80’s I was flying a red eye from Philly to San Fran on a United (I think) flight. There were 8 people on board. We each had our own flight attendant. You’ll never see that again.