I imagine they're waiting for the final level cap before really adding the endgame content. Or they may be planning to add quests or something to make the old content part of the new endgame. I kind of wish they'd start working on a FFXI-2 or something so they could add new regions. I know 14 has improved, but the flexibility of job change is what I like most.
I remember during FFXIV beta testing, everyone thought final release would be better and have more content...never happened. If they have plans to add a ton of stuff at 99 they would be showing it off not hiding it.