Bloodworms are excellent nutrition - high in protein. I don't know how the often repeated lore about them being poor food comes from, but it doesn't stand up to scrutiny. I've used bloodworm to condition breeders, something I can't do with any of the prepared pellet/flake food. The closest I get to success with prepared foods is with bug bites - black soldier fly based food, not unlike bloodworms for insect eaters.
If anything, bloodworms are used as a supplement because they are too rich. I bred a lot of fish using bloodworms 4-5 times per week, until I developed an allergy to them and stopped using them.
My niece has a Betta like yours - it won't recognize freeze dried bloodworms as food. It's clearly had nothing but pellets all its life, and she has given up trying to improve its diet. He is healthy, and what can you do? There are people who think McDonald's is as good as food gets, and maybe they get reincarnated as Bettas.