I on the other hand much prefer buttons on jeans. Not because of the failure thing (as others have said: That’s not much of an issue anymore) but because of how Zippers make the fabric behave and shape. A button fly conforms much better to my personal waist/crotch anatomy, especially when sitting. Undoing a button fly can be even faster than a zipper because you just have to pull in the right direction from the top once (instead of opening one button and then pulling the zipper). Closing is more involved but I can do it with one hand and without thinking actively about it, so it’s fine for me, personally.

Levi's had an advertising campaign in the UK a few decades ago that promoted their "new" button fly, so it's mainly a fashion/marketing thing. Jeans were around before zips were invented, so it's a callback to the original design.

I remember wearing them and certainly they were really stiff and awkward to use when new.

When Levi's first made jeans, zippers were not invented yet. You must have bought a pair from one of their original product lines.

Besides, pants with button fly have the distinctive advantage that you will never get your most sensitive skin accidentally pinched between the zippers. :)