+1, other banks/networks have a lot to learn from Amex in this regard.
AMEX is in a unique position. They have the most to gain with an SBS style promo as they have the highest interchange fees and the lowest merchant penetration. Just look and see how many jewish stores now take AMEX solely because of SBS. Plus AMEX gets to recoup a small chunk of the total amount spent due to high interchange fees.
Chase OTOH has lower interchange fees and top-notch merchant penetration via MC/VI.
For them they're better off offering better signup bonuses and more valuable points to attract more users that way.