Wood grain is like soda straws. As you know if you have an old piece of any wood and cut it, it’s pretty ‘clean’ inside. So called penetration of wood by stains, and such is very shallow.
Another old trick is to seal it with a different solvent product, like shellac. Another is get a couple of those two tubes injectors of epoxy at the hardware store, cut it with acetone, bush on a coat with a disposable brush, let dry and repeat again. You can top coat(s) with poly to make it look nice. I’ve done this with teak and mahogany on boats. Both can be or have had oils on them that just using poly causes either the finish to lift off in a film or not dry.