I sense creeping hyperbole. "Never been fiscally successful," without defining "success" is not a meaningful statement.
Has there been a time since the TSR days when D&D actually *lost* money? Not as far as we are aware.
Then let us be careful about how we talk about success and failure, and consider how Hasbro thinks about the brand in its context.
D&D makes a profit, but not a big one Hasbro's standards. So, there may be an opportunity cost involved - maybe Hasbro could turn those resources to some other product, and make more money. This is true. However, it also follows that if the cost to produce D&D is small, maybe turning those resources to another brand would yield only marginal returns.
Hasbro cannot sit on its laurels. It needs to keep a halo of less-than-breakaway-hit products around itself - because that's where breakaway hits come from. Hasbro is already in the business of holding stuff around, just in case. Hasbro's size and fairly hefty regular revenue streams mean that it can afford to be patient.
Moreover, many invoke this looming doom of Hasbro, without providing any solid evidence that Hasbro actually cares. WotC, by reports, still generally manages its own internal affairs, and has ever since Hasbro acquired it. Unless you have credible quotes or evidence to the contrary, it seems that Hasbro holds WotC to overall goals, but lets it try its own thing otherwise.
Now, if the apparently stable and extremely lucrative card game business were to collapse, then we might have a problem.
