TTRPG books are massively undervalued. The profit margins are non-existent, and creators get paid less than minimum wage for a book which took many people months or years to make, and which you can get months or years of use out of.
So, yeah, $70 doesn't pay for a hardcover TTRPG book.
WotC sells its core rules -- three books -- for, what $30 each? Depending on where you are in the world. But it's Hasbro and can print hundreds of thousands of them at a time, and so pays pittance for each book. And in doing so, trains the market what a hardcover TTRPG book is worth.
(This, incidentally, is why monopolies are generally prevented through regulation--unfortunately our little corner of the gaming industry is too tiny to qualify for notice, but make no mistake we are operating in the contrails of a monopoly, and the industry problems that causes are apparent).
The rest of the industry sells 0.1% of what Hasbro does if they're really lucky, and pays 10 times or more per book printed. And doesn't have worldwide distribution deals, if at all. And if they do have distribution deals, they're on much worse terms--like, 60% of the cover price is gone right there.
So a hardcover book? Really? For a non global-corp with massive economies of scale? It costs $100. That's minimum wage for the labour.
If you are paying less than $100 (and you are, because every company prices its books at $60 or so), it's because the company is not paying itself or its creators a living wage. Because they literally can't. And this is why the entire TTRPG entire industry is mainly people in their spare bedroom as a side job.
Sure, maybe the books aren't worth $100 to you. Maybe TTRPGs are not a viable business if you're not Hasbro. I'm not telling you what a TTRPG hardcover is worth to you... you spend your money how you want. Your priorities are yours. But I am telling you what it costs if people are paid fairly. And that's $100 for minimum wage.