If money could buy taste, a lot of the world would look better than it does. Culture isn’t a function of dollars, and we’re very lucky to have many people at Stripe who just really, really want to do great work.

(There is proof that significant financial resources aren't needed to do great work in a lot of personal websites. Most recent example I came across: https://bruno-simon.com.)

Money helps, but it's neither necessary nor sufficient.

I've been at a company that many considered to have excellent design and that received a lot of attention here (Heroku). There was a culture that permeated the company around beautiful design and what I would call "maker excellence". It was a place where people who liked building great things (both engineers and designers) felt at home.

Look at most of the biggest banks' website and their UI/UX is not even in the same league. I feel like stripe understood that their main clients are web geeks, so they are ready to pay the price and give the ressources needed for a good website.