They increase the cash back by 75% of whatever it already was. So if you were getting 3% back (currently, for their Cash Rewards card, that can be 1 of the following categories: gas, online shopping, dining, travel, drug stores, or home improvement/furnishings), you'd now be getting 5.25% back.

Which is a complete rip-off. You could easily get 2% interest on that $100k you're leaving with them by just leaving it with a better bank. For that to be worth it, you'd need to get at least $2k cash back on that credit card. At 5.25% (which is only for that 1 category you chose!) you'd need to burn through $38k/year... i.e., you gotta $100 a day on that card.

Except even if you somehow were planning to spend $100/day on that one lucky category, your cash back would be an order of magnitude lower, because they'd only give you that cash back on the first $2,500 in purchase, i.e. you could only earn $131 at most. So you're losing out on at least $2,000 to earn at most $131. Terrific deal!