Because it was. Now we're about 99% there. It's normal for the last 5-10% to take a bit longer than the rest, as there's a lot more hurdles to overcome and more unexpected issues that can arise.
As for your question about why it took so long: Alorth wrote a good bit of dialogue about this in a Discord announcement where he explained that the first two months of this chapter's development he was sick (due to a health condition, overworking himself at his regular job, etc)... not to mention having a breakup with his long-time girlfriend.
In general, this chapter is a bit of an anomaly/took longer than future chapters will, and there's various reasons for that. One such reason, as I've explained in the past, is that we wanted to take our time with it and not set a deadline for ourselves so that we could make sure we're living up to the insane levels of hype and anticipation that came after people played the first one.
And because we took our time with it, we've both improved greatly: the writing has improved, Alorth's animations are several times better than they used to be, etc. So in a way, taking our time with it paid off greatly. Now, I acknowledge/understand that it's not ideal to wait a few months for a new chapter, but generally speaking future chapters wont won't take longer than 3 months. Also, as I mentioned in the OP: Ch2 will be here soon; in the month of October.
You guys have my word on that!