It’s because of how identical particles and spacetime symmetry work — let’s unpack it.

In quantum physics:

• identical particles are indistinguishable
• exchanging two identical particles cannot produce a new physical state

So the state must be:

• unchanged, or
• changed only by a phase

Fermions are antisymmetry:

You may ask why fermions are antisymmetry, it relates to previous blogs elaborating this point at length, So exclusion is a consequence of spacetime structure.

In 3+1 dimensional relativistic quantum field theory:

• integer spin → bosons → symmetric
• half-integer spin → fermions → antisymmetric

How this makes matter solid?

Because:

• electrons cannot pile into the same state
• they must occupy higher-energy orbitals
• creates pressure against compression
• produces rigidity of matter

This is degeneracy pressure, not EM repulsion.