Why? The guild leaving penalties are there so that you don’t guild hop to abuse blood stones.
Also, if you only leave 1 guild in a 30 day period, the penalty is only 1 day. It only goes up as you join and leave more guilds in the same 30 day period.
So if you join and leave 15 guilds in a 30 day window, your leave penalty might be something like 30 days. This is probably higher because I think its 1 day, 3 days, 9 days, 27 days etc.
Its not based on donations or anything else. See below screen shot of my first character that has 51000 bloodstones and has been in the same guild since February: