When Google started, there were about 2 million websites on the web. When Facebook started, there were about 900 million people on the Internet. So both companies were able to solve problems at a smaller scale and grow alongside their user base. This is the product window.
The product window closes. It's why competing on a text-based social network against Twitter is hard. Or why there are no more Dropbox / Box startups. Sometimes existing companies take advantage of the product window (Intel pivoting from memory chips to CPUs, Adobe from licenses to SaaS).
Today, the price of a call to a large language model is $0.02 per 1000 tokens. Sometimes, you're given a small window to release a product and scale with your users.