Developers barely buy things. Excluding infrastructure, You can count with one hand fingers. Be it IDE, Password Manager, Note Talking, .. well I can't come up with things that they aren't already using FREE tools.

Excluding infrastructure is a pretty big exclusion, especially if your infrastructure includes tools like New Relic, Data Dog, Sentry, CircleCI, and the countless other developer B2B SaaS tools in place at thousands of companies. Most of those purchases were driven by developers even if not using their personal credit card to buy them.

Yeah, problem spaces of those tools left for indie SaaS to solve is pretty small.

where do you think are profitable areas for indie SaaS?

That's literally my question too, sorry!

We can build our own tools. Why buy any software, ever? Certainly, why buy software which is being advertised or marketed? There are business reasons, but not ethical or technical reasons.

Most people can also cook their own food, does that mean they never at a restaurant?