Snow Blocks, Powder Snow aren't a part of #azalea_root_replaceable / Rooted dirt can't replace Snow Blocks & Powder Snow

I can confirm this behavior. 

I can confirm this behavior in 1.18.1.

Here's a code analysis along with a potential fix regarding this issue. The following is based on a decompiled version of Minecraft 1.18.1 using MCP-Reborn. 🙂

Code Analysis:

net.minecraft.data.tags.BlockTagsProvider.java

...
this.tag(BlockTags.AZALEA_ROOT_REPLACEABLE).addTag(BlockTags.LUSH_GROUND_REPLACEABLE).addTag(BlockTags.TERRACOTTA).add(Blocks.RED_SAND);
...

If we look at the above class, we can see that snow blocks and powder snow and aren't included within the AZALEA_ROOT_REPLACEABLE block tag, meaning that rooted dirt cannot replace these blocks.

Potential Fix:

Simply adding Blocks.SNOW and Blocks.POWDER_SNOW within this block tag should resolve this problem. The correct line of code within its class should look something like the following:

net.minecraft.data.tags.BlockTagsProvider.java

...       this.tag(BlockTags.AZALEA_ROOT_REPLACEABLE).addTag(BlockTags.LUSH_GROUND_REPLACEABLE).addTag(BlockTags.TERRACOTTA).add(Blocks.SNOW_BLOCK).add(Blocks.POWDER_SNOW).add(Blocks.RED_SAND);
...