Donations only get you so far. Take a mid-sized project, that needs $500k per year (a few devs, very modestly paid, zero expenses). It's a lot of money. It requires a huge user base. Say you have 500k users, and 5% donate $25 per year (I'm optimistic). And that's just $500k US, a few devs, zero expenses. A project that size probably has audit requirements, hosting costs, accounting, legal, trademarks, etc.
I see finances for a few free software projects, and many of them really struggle to get donations year after year, in a way that helps make the project predictable and sustainable.
For the US, people want you to be a 501c3, and then you need a EU equivalent. Canadians are unlikely to give to a US org (especially these days), but the market is too small to setup a local charity. So you need partners. All that has many compliance requirements and paperwork, so you need non-tech employees for the fundraising and accounting.
Eventually your big donors start blackmailing the project if you don't do what they want, and often their interests are not aligned with most users. You need various income sources.