Athletes train to improve and will give up what doesn't produce results. If core work is beneficial to them they will do it.
Which is why cyclists and runner do minimal core work, and only after they are maxxing out their cycling-specific or run-specific (for running) training.
You do NOT see top guys going out endorsing serious x-training, even endurance-type x-training as a major part of their training that's taking an hour or more per day. You pretty much proved my point for me.