I don't know the details, but I've heard over the past few years, from relatives and family friends who work for CI.
Around 93-94, a relative who worked check-in at KHH commented that CI is looking to pull out from domestic routes.
On this forum, HKG and HND routes have been mentioned as the most profitable for CI.
As you may already know, the past few years have been a difficult time for airline industry in Taiwan. This may have also contributed to the "shrink".