The roots just seem to stick out of the sides while the trunk itself continues down in most of these, which looks strange. In some, you have the opposite problem, the trunk just ends in a few roots that don't look numerous enough to support a tree of that size.
If you google "tree roots", you'll get some photos and diagrams that demonstrate the structure of roots underground. Observe how the trunk widens into the root-mass, the roots don't look like they're just sticking out (with a few notable exceptions). Above-ground, we see the top of the root-mass, but the shape of it makes it clear we're not seeing everything. Note also how the trunk texture gives way to a different texture on the roots, it doesn't just continue down.
