While it may not fit to you, there was a case to be made for why it does indeed fit just fine. So, it all depends on the comparison you choose to make.
Rock, Sand, Salt, Tar, Scrap Bundle, etc - Resources
Branches, Twigs, Sap, Leaves, Cones, Seeds - Forestry
Grass - Foraging
I understood the forestry comparison, I listed it in my post.
Scav skill isn't hard to level at all, Forestry however is more difficult with trees being involved (tree limit, time to grow, etc) so it being a bit different from the others is completely understandable.