Originally Posted by
coke cans and winglets
It's most likely something to do with fare inventory. I was looking at MIA-SBN on Delta back in March and it wanted to send me MIA-ATL-MSP-SBN instead of just MIA-ATL-SBN and it was saying only First was available for $1800 one way.
Part of it is that Delta's RM algorithm doesn't believe in selling connecting flights (typical married segments are very suppressed compared to each segment alone).