The surface of the cut wood is “glazed”. Paint isn’t going to want to stick to it because it’s a very smooth surface and it’s impregnated with whatever organics cooked out when the laser got things it didn’t cut, hot. So the surface won’t “wet”, the paint’s surface tension wants to pull it away from the edges. Auto body primer will work but it requires a couple of light coats. If you lay it down thick, it behaves a lot like normal paint. Normal paint will do it, too, but it requires a lot of light coats. The best method I’ve found requires a little “elbow grease”, you have to at least lightly sand the glazed surface to rough it up so the paint has something to want to stick to… I have these little flappy-disk sanders that attach to a dremel makes quick work of it, can get in to most creases. Though if the edge has a lot of complexity I do it old school with a little strip of sandpaper.