IIRC the yarn developers worked with NPM to get it out. It's not a lack of will or ability on the part of NPM that it can't be "fixed", it's that NPM has just

IIRC the yarn developers worked with NPM to get it out. It's not a lack of will or ability on the part of NPM that it can't be "fixed", it's that NPM has just so much baggage. They can't change how things are installed, because that would mean getting rid of features that many people rely on. For a while they didn't even have any documentation on how NPM worked, it was a bit tautological (npm worked in the way that npm worked...). And rather than add flags or settings to NPM to support yarn's use cases which would bloat the code, add a pretty sizable increase to maintenance and support, and would really be a mess, they decided to create their own tool which is similar enough to make it easy to switch, but without any of the legacy baggage that NPM needs to support. It's a perfect example of the unix philosophy at work ("Don't hesitate to throw away the clumsy parts and rebuild them."), and just about everyone (including NPM) is happy with the work they are doing.