Let's assume that Boston Brand was wrong about the book sales numbers and Lindsay's books did perfectly fine. If that were the case, she would be boasting about it rather than slinking into a hole with her tail between her legs. If Lindsay's books had really done well, then she would certainly be using the success as a way to prop herself up as a pop culture critic expert. Lindsay did not want "okay maybe you broke even", she wanted motherfucking success. She wanted to humble-brag all over her social circles, so I think if her books had done even modestly she would have definitely mentioned it rather than act as if she'd rather we all forgot about this embarrassment.
They've done studies and shown that people remember less of a book if they only listen to an audio narration of it rather than actually reading the book. Which might explain why some of her fans didn't think her books were that bad. Or maybe they just read shitty books and are easily impressed. Unfortunately for Lindsay these simps are not high in numbers, hence the poor sales. Her redditors are blaming supply chain issues to get the third book printed off, which I'm skeptical about since I haven't heard of any other books releases being delayed for this reason (although it's always possible this is true, but it only affects Lindsay since her book is of such a low priority compared to almost every other author).
I might bite the bullet and read her third book, if only to see her laughable attempt at writing herself out of the corner she put herself in with the second book. I don't think she can pull it off, and even if she did it would still be a trilogy crippled by the first two books. The second book is a big enough roadblock to prevent anyone that's not one of her followers to pick up the third. She's going to drag her third book across the finish line, and her fans will drink their copium.
I'm not sure whether she or the publisher would rather give up and wash their hands of it, but I am certain she doesn't want to write this last book. Maybe it's the last of her bruised ego that's letting her finish or maybe it's shit tied up with her contract.