There is much lava in Nether.The lava valleys affect us to dig ancient debris.It'OK to have big lava lakes in the main world,but there is too much in Nether.We don't have it in earlier versions like 1.17.
1.17.1
1.18
MC-237017 Caves filled with lava below y=-64
MC-238949 Bedrock can be exposed to lava within lava-filled nether caves and ravines