Also, to add to this - the "dark ages" were kind of a misnomer. The center of culture and science in the West packed up and moved from Rome to Constantinople. What we think of as the "dark ages" were really the "barbarian" tribes of Europe (starting with the Franks), slowly becoming educated and cultured within the shadow of the old Roman empire.

Also, the monks and scribes creating palimpsest were not thoughtless. In the West we enjoy a very wide collection of ancient texts specifically through the diligent work of making and distributing copies. They were remarkably literate and intentional in their work.

A lot of these palimpsest were not entire books, but fragments or loose pages that had built up over centuries and then bound and repurposed. They were not any more sentimental with them than you would be with a pile of old journals from a thrift shop. A collection of celestial observations done by the eye were certainly not of particular interest to them.

Well 7-9th centuries were relatively dark in Constantinople as well, it took quite a while to recover from the Islamic invasions. It was just not a good period for Europe and the Mediterranean economically, demographically and politically.