History...?

It seems most interesting that we assume that all our technology and knowledge of philosophy, the world as well as the what happens. Has developed in the time since Jesus or even only the since the 1500 or 1600's. Now first of all we lost a great deal of knowledge after Christianity lost a great deal of knowledge due to book burnings or the simple ignoring of 'heathens' something that often happened over the course of history. The number zero was blasphemy in the eyes of the Christian church until the until the ealry 1800's (accounts may vary). The Romans used water supply and disposal that was beyond the ability of the Europeans of the until the mid-1800's since the greatest part of the European architecture was based on the trial and error system the dome in cologne for example partially collapsed several times while under construction due to mistakes that were well known to the preceding empires. The Chinese were far beyond anything that their European counter parts could offer in medicine, agricultural productivity and philosophy when they met each other. In fact many developments that were necessary for the European conquest came from China, like the compass. Now why is it that we often lack the understanding that we lost a great deal of knowledge during conquests and religious battles that we had to rediscover or find again, besides today's Math is based on a great deal of Greek theories, which were perceived thousands of years ago.
Why is it that some people still do not know or underestimate how dependent we are on the knowledge perceived long ago.
The same basic rule is true for religious account of the creation of the world, they often contain some event that actually happened maybe on a smaller proportion than displayed in the story but none the less.