Why does Firefox Developer Edition exist as a separate edition?

[jryans (J. Ryan Stinnett)]

Also, here is a similar thread on this topic:

Quantum - Beta vs Developer Edition

There was a thread a few months back about the Firefox Beta build vs Firefox Developer Edition. This was pre-Quantum and I was curious if there was honestly much difference between the new builds now? Feature wise in regards to DevTools, CSS Grid etc, they seem identical.