Okie dokie.

When sites asks for donations, it can for a number of obvious reasons. Paying for their website, buying manga/manhwa/whatever to be eventually translated, keeping up with scanning/editing/translating stuff etc. We may not even know if whatever is donated is guaranteed towards their scanning efforts, but I digress. Not everyone reads everything a group scanlates, so we don't know if what we're donating is necessarily going towards the series we want to read from the scanlator group. From what I've noticed, doujin groups largely take commissions, and it seems like they actively and regularly translate for commissioners. Your run of the mill scanning group (I assume) isn't going to drop what they're working on to scan something that you want, unless of course it's the next chapter of something and it was already on their list. I feel like they just go at their own pace (but why wouldn't they otherwise), whether or not someone's donation was meant to be for X series that they wanted to read. I would definitely want to donate (if I could) towards a series that interested me, but there's no guarantee that the chapters that I want to read would come out in a timely manner and would convenience me, the reader (but then you have groups like Mangastream that release lightning fast lol).