Except that most of the time, the people upset haven't paid a single cent towards that project. They make it sounds like they speak for the majority of people paying when in reality they've spoken with no one and the conclusions they make are completely insular. Just because the dev gets $300 a month does not mean you're giving him $300 a month. You're not entitled to $300 dollars worth of work paid by other people.
And unlike artists, there's usually an explicit agreement and expectation between the payment and the end product. Anyone who expects something in return needs to establish what they're paying for. If you haven't done that, then there's no obligation for something to be delivered in any timeframe. And inversely, you're a dumbass if you're doing unlimited work for unstable, subpar pay.
But let's pretend for a second that there was such an obligation, as ill defined as it is, for the sake of argument. How many work hours you you think needs to be put in between each release? How many work hours is $300 worth, assuming a fair wage? Mathmematically, how many months should this take, according to your calculation? If you haven't a clue, then what the fuck are you mad about?