Yeah, even as a huge Dragonlance fan, the poor sales of Fifth Age don't surprise me. Both the departure from AD&D as the main rules set for the setting, combined with the poorly executed "reboot" to it, I think it didn't create a product that was attractive to many OG Dragonlance fans. What may be even worse, the new Dragonlance was unrecognizable: one "boring" moon that doesn't grant magic, no gods—again!—and all this talk about a "Second Cataclysm" may just be too much.
In retrospect, SAGA may have been quite the decent RPG system for a heroic high fantasy setting as Dragonlance, but in the setting's OG form—with knights, wizards, and clerics—not in the dilapidated state we find it in the early Fifth Age.
Plus, "Dragon Overlords"—and the following Dragon Purge—may have been the most 90s and stupidest idea I've ever heard of in a fantasy context.