The net cannot be folded to form a pyramid because the faces that are not a base are not all triangles
If you fold this net up, you will get a triangular prism, NOT A PYRAMID.
A pyramid can have ANY polygon as its base, as long as all the other rest of the shapes are triangles.
Depending on the base, the number of triangles in a net of a pyramid must match the number of sides its particular base has.
For example, if you have a square pyramid turned into a net:
The base is a square (4 sides)
There should be 4 triangles on each side.
Because a pyramid is where all the triangles must meet up at a point.
Hope this helps!