How can any civilation exist for thousands of years but not have technologically advanced at all?

The short answer is, "Why should they have advanced?" We like to think of technological development as some static rate of change, or as a quantity which some invisible force pushes ever forward. In reality, we have no evidence or reason for this concept. When we ask questions like "How can they not have advanced?" we have to realize that we're expecting every society to behave like ours and, when they don't, looking for reasons to explain their deviation from a norm instead of discussing the factors that lead to how they really are. Imposing so much of what we think should be has no place in historical discourse, and the field is best suited to answer "Why," not "Why not?"

A lot has been written on this topic, so I would recommend taking a look at these two posts from /u/RioAbajo and a former user. They're a good introduction to why the concept of "technological advancement" is problematic.