Because the game ended up getting massive publicity it attracted a ton of people who aren't familiar with Early Access at all and have the same demands out of it as if it was an full release game, and so have thrown an entitled fit over the fact it is, indeed, an unfinished Early Access game and all that entails, such as shifting roadmaps and potential delays.
This isn't the fault of anyone but those people who ignored the Early Access disclaimers and came with unrealistic expectations and demands.

Compound that with the normal groups who want something entirely different out of a game than what it clearly is.

Finally online forums, and gaming forums in particular have an issue with toxic behavior because it is a low effort way to get attention that a whole generation of gamers picked up watching Streamers behave the same way. Negative news and sensationalism gets better ratings than positive level headed rational news and all that.