I thought I saw some threads on this but couldn't find them.

I'm looking at using my miles for flights from LHR to the US round trip. I was able to find coach tickets for 60k! However, every flight I price has taxes of at least $400 US! This seems like a horrible deal, as I am probably better redeeming for Amex gift cards to buy the flights and earn miles... but then how will I ever use those miles.

I then priced flights on United which came out to 55,000 miles and ~$150. For AA, they came out to 50,000 miles and ~$150.

How can Delta's taxes out of London for award tickets me more than 3 times as much as other carriers?