When you pay a fee to a website - do you question how they spend that money to this level of detail? Do you ask, I dunno, lets go with Slack, to break down their fee by how much of it is necessary to keep Slack online "as is"?
I don't think I've ever seen someone do that. There's a level of entitlement that comes with donations that people just don't attach to services they purchase.
Wikipedia isn't a charity in the traditional sense - IE it's not taking those donations and redistributing them to those in poverty.
It's an organization building and maintaining a platform that provides pretty a vital service to society. Almost everyone who donates to it will have gotten far more value from Wikipedia than the cost of their donation. Maybe, instead of thinking of it as "donation", people should be thinking of their contributions as a "sliding scale fee".
On the other hand, I do believe Wikipedia should be open and should be accountable to its community. I just believe the community should be reasonable when exercising that accountability.