Why is the "denn" not translated?
It's a modal particle. There's no exact equivalent in English, so it's best to omit it.
Thanks, the page you liked is great!
Very helpful link! I often don't know what to do with these particles, but now I have a reference. Thank you!
"What do they offer because" what does this mean? Why not just "was bieten sie an"?
How would you express "what do they offer, then?" in German?
then = dann, where as denn = because.
Your sentence would most probably be "Was bieten sie dann an?"