All too often on Hacker News, I come across a comment like this:
wouldn't most of them be able to build something like this for internal use in a single day
Yes. Of course, it might only take a day to build, but it will be maintained forever. And that means dealing with potential bugs. That means testing. That means deploying. It means having a way to manage it. A way to scale it up. This means adding features as needed. And of course, still dealing with new bugs. It's another system, another cog that you have to maintain.
So, next time you need to create a tool like this, stop and think for a moment. Is this built? Does this exist out there? If so, consider using the service. However, if what you need doesn't exist, than maybe, just maybe, you've found yourself a new idea.