[BenLurkin]

"If a spaceship has loose, damaged or missing tiles, that can change the aerodynamics of the ship and warp or melt the underlying aluminum airframe, causing nearby tiles to peel off in a chain reaction. If the tiles start stripping off in large numbers or in crucial spots, a spacecraft can overheat, break up and plunge to Earth in a shower of hot metal, much like Russia's Mir space station did in 2001."

Looks to be the sad explanation.

[Sub-Driver]

like a zipper effect...........BTW, they usually do NOT examine the craft during spacewalks, they work out of the bay......