In short, it may be nice to provide a simple package install for the bulk, but it makes it an unnecessary chore for others to produce simple alternate environments.
arcpy 3.0 py39_arcgispro_36030
------------------------------
file name : arcpy-3.0-py39_arcgispro_36030.tar.bz2
name : arcpy
version : 3.0
build : py39_arcgispro_36030
build number: 36030
size : 5.4 MB
subdir : win-64
url : https://conda.anaconda.org/esri/win-64/arcpy-3.0-py39_arcgispro_36030.tar.bz2
md5 : 539ed0c88f7227faf15e91f34f0bd21c
timestamp : 2022-05-27 19:30:14 UTC
dependencies:
- arcgis 2.0.1.*
- arcgispro 3.0.*
- asn1crypto
- azure-storage-blob
.... huge snip
There is no reason for it related to arcpy specifically, in fact it is the other way around (or shapely).
Better still "arcgisscripting" would be nice to package/install on its own.