I think for a lot of people it’s a mix of places.
We are having a 19-month engagement in order to put aside money every month, and have modified our usual budget to spend less on other things. For example, no weekend trips, eating at home more, etc.
When that wasn’t allowing me to accumulate savings fast enough, I got a new, higher-paying job. Seriously. It was time for me to start looking anyway, because I knew I was underpaid, but I liked my old job. Saving for the wedding was the kick in the butt I needed to upgrade my career.
Our parents are very generously funding about a quarter of the total expenses. This seems to still be a thing many parents do? We didn’t expect any contributions and it was a total (recent) surprise— both my partner and I paid our own way through college and come from families where the ethos is very much “once you’re 18 you should be financially independent”.