They already use these bomb detectors on some bags with random checks. Apparently these scanners can detect any residue of explosives. Why not make it compulsar

They already use these bomb detectors on some bags with random checks. Apparently these scanners can detect any residue of explosives. Why not make it compulsary for all laptops? Should be impossible to transform a laptop into a bomb without creating some residue. Or are they concerned that people use batteries as bombs? In that case you could just use several phones instead.