It's an excellent example of trends feeding consumer expectations feeding trends. It's a self-fulfilling cycle.

I think it's the same reason why marketing websites for many SaaS products all look very similar. A product like Stripe with a very nice marketing site becomes successful, many other companies follow suit and copy the style. The style becomes ubiquitous. "This is a SaaS product website".

The same could be said about a lot of consumer products...cars, laptops, phones, food packaging, even art and music. There's so much stylistic homogeneity. Obviously part of it is fashion, but what is fashion except consumer expectation?