- Why do we have to reach a friggin' stretch goal to be able to purchase additional content? There's no way I get this thing without getting EVERYTHING...
Principally I agree with you: I think SGs to unlock add-ons are a waste. If the sculpt in question incurs additional tooling costs, though, as steel moulds are expensive to produce, then it makes sense. That said, if they combine all add-on minis in the same mould it wouldn't be a per-piece tooling cost and the answer becomes "because they can".
However, I'd like to point out that SPM has an excellent track record for communicating and honesty with their fans/customers and I wouldn't simply write them off as greedy.