He wasn't dismissive, he was countering dismissiveness. It was dismissive to throw out "just build your own". 99% of companies don't have that option, most companies are customers, not builders. This commenter was pointing out the obvious lack of perspective on the majority of businesses. That is a huge problem in SV and software development these days, the lack of awareness and context about real problems out in the market. "Just build a replacement" is a non-viable route for most people and most companies.