You don’t - it’s a bullshit excuse. It’s like a 5 year old with their hand in the cookie jar saying “I didn’t mean to do it.” Yes you did, little Jimmy, what you didn’t mean to do was get caught. Now blow that idea up to a greedy, unethical, billion dollar corporation.
Those would be mad expensive too - think about all the awesome D&D video games that have ever been made. Yes they’ve been less so in the last decade, but any company would know the power of the name and want the game rights as well as the printed media and other rights. It’s a whole deal. Larian could almost never hope to have the kind of money that would convince Hasbro to sell the game rights separately, much as we’d basically all prefer that.