Why not simply say donation
It’s about setting expectations. The wording is chosen because they believe that paying open source developers for their work should be the norm, not the exception. Calling it a donation would not do that justice. Their wording is saying “Here’s the software, we’ll trust you to pay us for it if it brings you value and you can afford it”. It’s an explicit expectation to pay, unless you have good reasons not to, which is also fine but should be the exception. Whereas a donation is very much optional and not the default expectation by nature.
In the end it’s just a semantic difference, it’s just all about making expectations clear even if there is no enforcement around them.
Just so you know, the GDPR mandates that you can at any time get a full export of all your personal data from anyone who’s processing it in a common, machine readable format. It is laudable though to have that integrated as a feature in the software, rather than jumping through hoops contacting support etc.