The article literally mentions full time work in the first sentence, and multiple times later.
> we settled on $11,000 per month as a baseline salary for working full-time on open source
The people getting $2,000 per month are part-time:
> a "part-time" rate: we could initially afford $2,000 USD per month.
It is also explained that if possible, they would go full-time and the salary would then be raised to "the full-time rate".
> Our hope was by announcing this plan and continuing our fundraising efforts, we would be able to increase the budget and raise them to the full-time rate.
I think I know why they're running out of money!
Seriously that's an amazing salary in 99% of the world for working on commercial software where you don't get to decide what to do, can't remote work, probably aren't working on your passion project, etc. etc.