I think what may made CX hesistant on B748 is the decrease in cargo revenue. CX has significant drop in cargo traffic due to China being more open and more cargo are shipped directly into China, and HK by itself simply doesn't sustain enough demand for CX to count on cargo revenue increasing year after year. If CX can't count on cargo traffic to go up, there's little reason to go after the B748s as B773ERs are the best fuel-efficient planes for long-haul traffic.