Since you query for opinions I think that it is mostly economics to have the caustic tower at the high pressure end to reduce diameter. I think that a consideration for not having caustic scrubbing altogether after compression is to reduce water load on the driers via the compressor and its aftercoolers.
Its been several years since I worked in an ethylene plant, but this is what I think may lead to this common design. Others may have a even better reasoning.
best wishes,
sshep