The author here.

You are right. I basically build my apps for myself who always use the same computers. I understand there are various people with various needs - but I would like to focus on pleasing people who are similar to me. I believe this is important to provide a good service. I don't feel like making apps like Microsoft Office with tons of features to please everyone.

The platform you develop on isn't a feature. It's a platform - and without a doubt, a web app is the most ubiquitous kind of app that can serve anyone on practically any internet-connected device.

Internet-connected is the key term here, though. If your target audience are internet-less note takers, then a desktop app is the correct choice.

If you don’t log into personal accounts on it what difference would it make if there was a web app version of this notes thing? You wouldn’t log into it anyway.

Presumably, they mean log into personal desktop accounts (as in "at a login prompt" or "what would change the output of `whoami`") rather than into a personal account on a website within a browser session.