This map gives me many lore questions like... why is a third of the galaxy simply left as "here be monsters" unexplored? What is the meanings with the different rings of the bullseye? Who are the corporate people int he corporate sector? how are they different from other lawlessness?
I guess there are many comics and books to read and fill those voids.
IIRC, the Unknown Regions were, well, mostly unknown, as a countermeasure: to contain a powerful evil known as Abeloth. So stable hyperspace lanes into that region are very few and far between, and only few folks like the Chiss (Thrawn's species) inhabit that chunk of the galaxy.
The Corporate Sector is an old creation from a series of Han Solo novels published in the 80's. The vast majority of those worlds come from ALL of the expanded universe (novels, comics, games) pre and post Disney across many decades.