[MichaelGG]

Winner take all maximises the influence an individual state has. Viewing it from the point of one state, if their citizens want candidate A 51-49, it only makes sense to throw all their votes towards it. Awarding proportionately would mean the decision is up to other states. Swing states would lose all their power as you could count on them being nearly perfectly divided.

Now if you want to abolish the states and just have one federal government you'd have a point, but that's a whole different issue.