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.
I suspect the reasoning for it was more along the lines of “if you’re pasting the password, that means you probably saved it in a text file on your desktop or something, and you shouldn’t do that so let’s stop you from doing it”. In reality, it probably didn’t work to make anyone store passwords more securely, and only made life unnecessarily harder for people with password managers