In the FCC filings I read, they blamed it on lack of donations.
This was back when they had one channel. It was the most difficult, alienating channel to watch on the dial. I don't think TBN even watched it. They've since put effort into their programs and have a better product.
If I remember correctly, they sold many of the LPTV stations to smaller operators, like RetroTV. Many never made it back to the air and have since been deleted.
OTA TV has experienced a bit of a comeback since they exited the LPTV game. You have to wonder if they still came ahead in the longterm with the scale back.