A port that supports 100W power input requires a significant amount of external components. Switching that between locations is also a significant challenge (IOW, it costs significant money and space). Just switching between the wall and the battery is hard enough, adding a third location will add a significant amount of space and $.

It will also add significant protection costs: what if somebody plugs 2 chargers into the laptop? They'll be at almost but not the same voltage, and amperage levels will be high enough that significant damage could result. Obviously the laptop will only do the upgrade voltage & amperage handshake with one of the chargers, but I imagine that redundant hardware protection will also be required.