Why does meat coated in oil cook better than meat not coated in oil? I recently oven cooked some meat.  Half was coated in oil the other half not.  Other than that they had salt and no other ingredients.

After cooking for about an hour I found the one coated in oil had less crusty surface and wasnt tough whereas the one with no oil was tougher inside and had more crust on the surface.

Why exactly is the oil doing that made the food come out this way and basically cook better?
What meat ? (beef, lamb, pork, chicken ? )

Oil (fat) facilitate heat transfer.

If your meat does not have oil on it, I assume it will dry out when baking.

Sometimes drying out is a good result ( crispy chicken skin, pork crackling... )