For-profit customizations (via an extension) may want to fork to avoid competitive situations such as e.g. the multi-year struggle between uBlock Origin extension and Google:
Not for-profit may fare better, tolerating and pivoting as corporate owners attempt to strategically vendor-lock-in new markets, presented to e.g. Google by the innovators of the extension.
Putting your brand name on the primary application users interact with on a computer is probably a few billion times more valuable than an extension in a thing under someone else's brand.
It appears to me like they're posturing to investors on the AI hype train. Publishing an extension isn't as sexy or "grand" as shipping a browser.