It may just be a paranoid delusion, but I'm worried that Babel is trying to become a more encompassing build tool ala Grunt/Gulp instead of just transpiling. I love Babel and plan to continue to use it in the future for my front-end development, but the "doing it all ourselves" is a little bit much.

I would much rather see a recommendation and efforts around Uglify than a brand new minimization tool, and I would rather see work on acorn[1] rather than around a new parser[2], because these things fragment the community rather than bring them together.

Edit: Yes, Uglify has taken a long time to get work done on ES2015, but note that the spec has changed a lot over that time. It does feel like they are dragging their feet or not getting much done in that front, but all the more reason to put one of the Babel devs who may have more free time on the project to get more things going.

1: https://github.com/marijnh/acorn

2: https://github.com/babel/babylon

At least when it comes to parsers, it makes sense for Babel to want to be "in control" of their destiny here. Its really hard to draw a line between transpiling and parsing, especially when many of the features you are implementing require new syntax. Not having your own parser can make this more difficult (especially considering how unfortunately most "production ready" parsers end up being hand rolled so don't really easily allow "plugins" or "composition" to easily add new syntax). As babel may aim to implement experimental features that may never actually be added to JavaScript, it would be understandable that that may be considered a low priority for a standalone JavaScript parser project while high priority for a transpiling project.

But my point still stands -- why don't they just work with the acorn developers to get specific features rather than build their own?

Yeah there's multiple JavaScript parsers: esprima, acorn, shift, babylon (uglify has their own parser I think).

There was an effort to standardize as well in https://github.com/estree/estree.

EDIT:

However, in Babel 6 there were a few (nice) incompatible changes to the AST which was unfortunate for interop and other tools (https://github.com/babel/babel-eslint had to make a lot of changes).

I don't want to speak for him, but I think a lot of the decisions to fork (parser, etc) at the time were most likely made like mentioned above to move faster. And at the time, Sebastian was basically the only one working on it. Maybe more context from his post: https://medium.com/@sebmck/2015-in-review-51ac7035e272#.qcyz...