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?
1. Clearly cares. Does great work.
2. Industry is like "damn this guy does great work, do ours".
3. Consumers get used to the style. Begins to become a standard.
4. Becomes an expectation, almost like a seal of approval. "This is a ski resort".