There was no reasonable explanation given as to why all the extra content couldn't just be in another update.
That's kind of the whole thing... He could have made 1.9 and then 1.9.1; 1.9.2; 1.9A or whatever for the extra content. Like he has done several times prior.
Instead it turned into scope creep and all the deadlines passed without any real reason for them to. He could have done half of the work, released that, then did the other half and released that. Same timeline, same work done, just more releases for the people to enjoy.
If anything he might be creating more work doing it all at once if there is no proper version control etc. since more bugs might slip in that become harder to track and resolve. Considering he's also revising old content at the same time it might become a complete soup. I'm sure he's a competent dev and it'll all be fine in the end but you can't help but worry about it at least a little. Especially with the deadline eventually turning into 'It'll be finished whenever it is'. For a lot of people that's seen as a red flag in content development. (for the record I'm not saying it actually is one in this case.)
As for the 'more content' a lot of it has historically been catered to a very small minority shouting loudly on discord to have it. The majority of players might not ever even interact with it (or be averse to it). So the update having that as an extra or not doesn't really matter to them. That's kind of besides the point though... Since we haven't really been told much about what's actually being added as extra content aside from the planned content, it's difficult to say what to expect. (In all fairness, I, like a lot of other people no doubt, also haven't dug much deeper than what has been publicly posted here and there, so there might be things I'm not aware of)
If there were at least some more explanations/updates or teasers of what is actually coming, I don't think it would have ever reached this point of malcontent, to be honest.