In practice it's not that easy.

For example, you might have a problem that is worth solving just for yourself alone. In that case, you might wonder if it's worth creating a web UI around it or a simple script suffices. That depends on other people being interested on it or not.

Another case could be that you want to learn more about the problem before designing the solution. Should you really create a bad solution just to get in contact with the people that have that problem?

It's usually easier when people reach out to you for help with a problem they're desperate about. Instead of you cold-emailing randomly.

That's more or less the spirit of starting just with a landing page.

What's your opinion?