To a lot of MSers, including me, amex accounts are very valuable for the sync offers that are potentially huge MMs. Depending on how many primary cards and AUs one has, not counting S/BB prepaids they have, they can rack up substantial rewards. For certain offers that can be used at certain merchants that sell VGCs, these can be very profitable. There are people I know who buy eGCs from participating merchants that they resell immediately.
It really depends on each one and how they use their cards to their advantage plus all the tricks being shared by certain groups.