I'm surprised it's baffling in a community of developers and other IT professionals.
It's not baffling to me that two significantly (wholly?) different applications on different platforms and form factors would require quite a bit of work to both be generally compatible with the same third-party software via the same API - and all while maintaining the same compatibility with another application, made by another company, completely outside Mozilla's control.
And it needs to work reliably enough to release to a world of developers - of every skill level, motivation, writing every kind of software (within the domain of browser add-ons) - with confidence that it will work for them and users.
And you need a way to maintain all that over the long term.
I'm impressed Mozilla!