They do have uniforms, they just don't use them because it's way more effective to have Schrodinger super-position civilians who are soldiers when a gun is in their hand, and innocent civilians when they drop the gun.

Also, Hamas's leaders are worth over $10 billion collectively. They can at least afford basic uniforms and spray paint to mark their vehicles. But again, they won't do it, because civilian deaths are the last piece they have left for international support. Which comes in the form of aid, which they seize, and pad their $10 billion with.