Why are some HITs, that are weeks old, which consistently states that "there's no more available" are permanently visible on mturk for weeks on end? The requester hasn't taken them down. Just because
you see no more tasks, doesn't mean there are no more tasks. Just no more tasks for you.(There could be no more tasks though) Either way, the requester hasn't taken down the job. And, if there's more work to be done and nobody is doing it, it's because the pay sucks.
and then there's some HITs like the one above, which disappears seconds after they are posted?
These are good paying HITs and also not usually batches. Like HelloHello said, good stuff gets scooped up quick.