"Funding" isn't really a good answer IMO. I don't know a ton about Fusion research specifically, but NASA is horrifically inefficient with money compared to private competitors. Giving them more money won't magically make them more efficient. Reasons why include:

- Their incentive is to optimize for political approval, which means spreading facilities among as many congressional districts as possible, which creates a ton of inefficiency from poor communication and the need to constantly ship things around

- Public approval is the goal and failure is the worst possible option, so things tend to be optimized to take as few engineering risks as possible and have huge amounts of bureaucracy to spread the blame for any possible failure

There's a reason why SpaceX started landing rockets with a fraction of the money that NASA spent on building ridiculous boondoggles.