Why do they use symbols and ideas from ancient Egypt?

Because they are nostalgists, obsessed with tradition, the “old guard”, and the old hierarchies. Basically the same reason that fraternities use/worship ancient greek.

Is this an unbroken lineage/ideology that has lasted since those times?

It’s highly unlikely. It’s probably a “resurgence” / “reappropriation” at some point in the past (perhaps even several centuries ago) like the modern day druids. Occult cosplay.

Wtf is really going on?

As general as possible - i suspect it all to be a test. More specifically it is a group of callous, ignorant [evil] slavers mindlessly enslaving their own kind for shortsighted perceived (but not actual) personal gain.