There is absolutely a reason. It's a service and many people (myself included) don't want to download a desktop app to use it.

He's not asking for your SSN or your address. If you want to use a burner email and a VPN or enter fake data to try it out, you can. This hardline approach of "every service should be an open source desktop app that I can run with zero telemetry from my cabin in the woods with no internet" so often found on HN is clearly not the opinion of the majority of internet users.