maybe to match different people preference
assume, in my old pentax DSLR, there are no AE Lock link to the half pressed shutter, while on Olympus DSLR, it always AEL on the half pressed shutter.
so people using pentax may get annoying with the AEL shutter button on Olympus and vice versa.
having an AE instead of AE-L have benefit that you can see or watch the how the composition change the metering value, so you can judge the metering better than it locked by default. for me myself, I prefer AE and adjust the metering by exposure compensation rather than to nail the exposure by AE-L.
just my 2 cents
