Why do people in early 20th C films put 1 foot on a pushbike..

[YokohamaSapphire]

..Instead of tilting the bike at 45°, mounting it then heading off? Also, they always seem to be wearing big overcoats

I used to do this when I was in school as we cycled everywhere. Now I wouldn't, I have to cross the bike before I push with the pedal.
The last time I was on a bike was a few months ago and I was knocked off it in the cycle lane so I doubt I'll be cycling again any time soon. Unfortunately.

I found a video “7
magnificent ways to mount your bicycle” and I now understand what op was referencing. It included the 45 degree technique which I have never seen IRL, but also the pedal push off the op described and it looked awful.