Their accountants probably prefer this route though. They don't get a competitive advantage by have a proprietary license, so open source is a good choice, but the GPL has issues they want to avoid. By going this route they can use tax breaks that are not available for doing the work in house. Sure it is more complex, but the results matter, and the result they are hoping for is someone else does work that they don't pay for.

Also it's probably cheaper to fund an OS developer for a year than paying for lunch alone for their own engineers.

What kinds of tax breaks are available for the case of using consultants instead of employees?

It isn't consultants it is 501 charities doing the work. The charity hires the consultants.

There are a lot of tricks needed to make the above work, and details that you need to consult a lawyer and accountant for.

> they're quite capable of assigning their own engineers

but if they develop it for internal usage only, then they don't get the added benefit of destroying the existing copylefted version!