It isn't a scam per se. It will be a scam if you decide to invest external currency into it. Barring that, it is a pump and dump, used exactly as you described it.

By itself, Steem is a garbage cryptocurrency. But as a medium of exchange via blog posts, it has gained value (kind of like cacao beans thousands of years ago, or anything in demand but lacking intrinsic value). The sole purpose it has value now is precisely so it can be pumped and dumped for BTC on crypto exchanges.

The major external cost is your time. When your payout doesn't adequately compensate you for your time, then it's either time to stop, or to stop expecting to profit.