In early snapshots, they simply extended the build limit upwards like you suggested, so when people loaded their old worlds in they started complaining about kilometer-high walls generating in every direction
That would lead to playering being able to accidentally mine themselves off a cliff and throw themselves into the void. You’re not supposed to get under the bedrock.
Why would they move the bottom of the world below 0 instead of just moving sea level upwards?
Compatibility with existing worlds
In early snapshots, they simply extended the build limit upwards like you suggested, so when people loaded their old worlds in they started complaining about kilometer-high walls generating in every direction
Why didn’t they just move all the old stuff up?
that would require moving every single thing up which would break a lot of stuff like mod/plugin data
That would lead to playering being able to accidentally mine themselves off a cliff and throw themselves into the void. You’re not supposed to get under the bedrock.
Why didn’t they just put more bedrock under the old stuff?
That would probably cause a lot of lag and bugs