ANB/TEN game designer revealed free flight was planned as early as A New Beginning

According to the late Cameron Davis, game designer of ANB and TEN, Sierra pushed for free flight to be added in A New Beginning, but Krome Studios didn't have the hardware for it at the time, and doing so would require redoing the combat system and level design already set up.

Cameron: Honestly I feel like us saying "we can't do flying" was probably the biggest reason we didn't get the third game. The publishers just would NOT shut up about wanting this (yet insisted on other factors that made free flight basically impossible on the target hardware) [...] The main one (factor) I remember is that being able to fly at any time meant that you could skip most of the encounters, which meant we'd need to change the enemies, which meant we'd need to change the combat system, which meant we'd need to change the whole level design etc etc. Just cascading on and on.