1993 is awfully late. I understand by that point virtually the whole country was on ESS which of course supported both.
Independent companies serving small exchanges were especially anxious to switch over since the maintenance savings were very significant. For SxS, they had to send a man out to add/change/delete a number, but I think on ESS the computer handled that automatically; that is, the distributing frame was automated. ESS of course required lower physical maintenance, too.
Some rural areas were growing very rapidly and a new exchange was needed. ESS allowed re-use of an existing building instead of building an extension.