I think most of the people who sign up for email alerts would never pay. Lots of them are indie hackers or folks with a side project - I've been there, and know how price sensitive those communities are. I'd rather they use the service for free than not at all - I get valuable feedback from that, a marketing boost if they tell others about it, and the validation of having built something other people use.

I do have a paid plan for people who want Slack notifications, and I think those folks ought to be happy to pay. My hope is that I'll eventually get a few paid signups and that those will cover the costs of the service (which are minimal).

I know I lose a bit of revenue with the above approach, but it's a tradeoff I'm happy to make.