The problem is that it's not clear which is "inferior" and "superior" and it may not be for another ______ months/ years.
Bitcoin cash may have bigger blocks/ faster transactions but it also has something like 5% of bitcoin's miners, so bitcoin is clearly the more secure coin at the moment.
It makes it easier to ROI when there's only one option. Should these bitcoins continue to split in the future, we may have to hold tens of versions of bitcoin in order to hedge against the unsuccessful chains.