I just don't understand five years development if it's mostly the same map.
I feel like designing the open world map is a huge part of dev time.
I don't think they spend 5 years on it actually.
They announced it in 2019 and were supposed to release it 2021/2022 but it moved to 2023.
Apart from the pandemic it seems to have been a matter of development priorities. Monolith Soft helped out on this game and a bunch of other titles and the Zelda team did some side projects too.
Age of Calamity came first, Splatoon 3 next, then Xenoblade 3 and now Tears of the Kingdom. Up next is Pikmin 4.
The game pretty much remained the same from its first reveal to the latest trailer. Fujibayashi knows how to stick to a plan, Aonuma was much different, he would announce Wind Waker 2 and ended up shipping Twilight Princess.
In this case it seems they've just been steadily working on it until they could free up enough resources from other projects for the final stretch. Not having to ship with new hardware or any particular holiday season probably helped with that.
In terms of the map it seems like they poured more resources into creating 'dungeon-like' environments, the sky islands, new enemies, quests, story, cutscenes, bosses etc. . A new map probably would've meant BOTW on a new map, while reusing assets actually means more changes were possible in the other areas of the game. It reminds me of Super Mario Galaxy 2, which was basically a Super Mario Galaxy expansion, but holy fuck was it good.