>>718442639 (OP)
It was just the era. The fact was Japan was intensely ill-prepared to deal with the sudden dramatic rise in power during the 6th gen. In order to save on time and costs, they had to get rid of a ton of JRPG mainstays. In FF9, the overworld wasn't all that complex. Just simple textures over basic polygons most of the time. But the graphical capabilities of the PS2 were dozens of times greater than that of the PS1, and such cheap-looking overworlds wouldn't fly. This is why so many JRPGs of the time got rid of them. Additionally, there was the increased expectation for voice-acting.
A few JRPGs managed to avoid the issues by scaling back graphics. Tales of Symphonia wasn't an especially pretty-looking game so it managed to keep some semblance of an overworld without going TOO overboard in terms of costs. But a lot of devs just sort of gave up and resorted to linearity as a cost-saving measure. Capcom's Breath of Fire series also got hit hard by this, with the last console entry of the series, Dragon Quarter, being an extremely short and hyper-linear game.