Vegas has a lot of big buildings right out there in the middle of the desert.
Of course they need to set lines where people will bet but, if there's something outrageous out there, they won't be able to build more big buildings in the desert.
To put it another way, Baltimore had a fantastic year. However, their record in close games was amazing. THAT won't happen again. And THAT'S what's driving the lines not dumbass Red Sux fans.