Re: It's quite clear where the money is:
@doublelayer - Interestingly, the one point your Charity director didn't raise was funding. In my experience, many charities can not only get really cheap products from companies such as MS and Cisco (see https://www.charitydigitalexchange.org/ ) but also many donors are happy to fund capex as it is 'tangible', opex on the otherhand...
The other objection I've had is the perception (not totally invalid) that they have reduced support options available, whereas with MS for example, there are plenty of businesses with relevant experience, so if their IT consultant falls under a bus or succumbs to CoViD19...
As for your other points, I think whilst much has progressed since XP went EoL, the free software alternatives still have some way to go before they really are enterprise ready. However, the world isn't standing still and so business is in general signing up to the product sets that are familiar to them...
@AC - Don't disagree with your experience, particularly given how entrenched products from MS, Oracle et al are..