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.
I’ve had many hundreds of hours of Minecraft these past few years but… What’s layer 4?
Y-level. Before 1.18 the top layer containing bedrock (ETA: in the overworld) was y=4.
Technically, the top layer bedrock can spawn at is either y=128(the nether roof) or the top of the obsidian towers in the main end island
They changed the height of bedrock?
bedrock now spawns around Y=-60, give or take a few blocks
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