My guess is that it's seems rather complicated and intimidating to non-tech users. I've been using and testing Notion for a while but when I consider my non-tech-savvy colleagues I imagine I'd have a much easier time explaining Basecamp and Airtable to them. Airtable feels more inviting compared to Notion.

Or put differently: I think we overlook how many people might be overwhelmed with building their very own specific todo list in something like Notion or to a lesser degree Airtable, compared to a solution that provides a fixed, rigid set of fields.

Airtable is web-based, Notion is for desktop use with Windows and macOS clients.

I use neither of them but my preference goes to the web since I work on Linux.

Notion has a web application you can use, no need to download.