Well, with these "high spend for bonus" cards you either need to buy them just before a pre-planned big purchase (car or holiday), have high ongoing reimbursed costs (work travel expenses you pay for then get paid back), or bring forward regular spending (manufactured spend, so buying gift cards or stocking up on supplies).
As others have mentioned, I would think the credit card companies are getting wise to the trick of buying gift cards, though your provider may still allow it.