Funny, the further back to you go with airline schedules the more they were structered like train timetables, (since that is who they learned from). They even had schedules reading "up" amd "down". Planes made more stops back then, etc.
Pressurized jet airplanes get terrible fuel economy at low altitudes, which is a reason why avoiding intermediate stops becomes desireable. I think this was much less of a problem for unpressurized piston planes that were common before about WWII.
A modern pressurized jet at cruise altitude and speed also probably goes 2-4 times faster than a DC-3. And the takeoff/landing process hasn't gotten any faster (if anything, it has probably gotten a lot slower, between airport congestion and the larger altitude changes now used). So those extra stops would have a much bigger impact, percentagewise, on the time the trip takes than they used to. It's probably now faster to take a direct flight to a hub even if that hub is a little out of the way than it would be to make extra intermediate landings to get to a hub fewer miles away.
I suspect a typical modern jet also can carry enough fuel to give it a much longer range than those older planes had. I suspect a DC-3 full of passengers simply cannot carry enough fuel to make a trip from New York to Los Angeles without stopping for fuel. (Yes, I'm using the present tense here. A private pilot who is willing to spend a couple thousand dollars can still find flying DC-3s on which to get a DC-3 type rating. It's even possible to spend about $4 million to get a remanufactured DC-3 with turboprop engines, and apparently for certain kinds of cargo carrying, etc, that makes a lot of sense even today.)