The reality of a project like this is that to get it right (which is by the creator's standards, no one else's) takes time. Add on top of that Blow and Thekla are building games with this to dogfood it which takes time, too.
Sadly, there exists a breed of developer that is manipulative, obnoxious, and loves to waste time/denigrate someone building something. Relatively few people are genuinely interested (like the OP) in helping to develop the thing, test builds, etc. Most just want to make contributions for their Github profile (assuming OSS) or exercise their internal demons by projecting their insecurities onto someone else.
From all of the JB content I've seen/read, this is a rough approximation of his position. It's far less stressful to just work on the idea in relative isolation until it's ready (by whatever standard) than to deal with the random chaos of letting anyone and everyone in.
This [1] is worth listening to (suspending cynicism) to get at the "why" (my editorialization, not JB).
Personally, I wish more people working on stuff were like this. It makes me far more likely to adopt it when it is ready because I can trust that the appropriate time was put in to building it.
[1] https://www.youtube.com/watch?v=ZY0ZmeYmyjU