> On Reddit this means that I manage to close the thread by accident all the time because someone thought it would be a good idea to open the threads in a modal that closes when you click outside of it.

The whole point of modals is to enable the user to close them by clicking outside of them. So this way if you want to show new users something like an onboarding tutorial, they can just click outside of the modal if they are like "WTF is this??", rather than needing to look for the close button. The fact that many people abuse them doesn't negate the fact that they are, if used correctly, actually a better experience for the user.