Dish's logic is always motivated by $$ (even if only perceived), so I expect it's a combination of the DMAs where they tend to gain the most new upgrades to analog LiLs minus whatever it costs them to get rights for HD feeds.
Because there's no additional charge when the HD LiLs are added to a customer's existing SD LiLs package, Dish only makes money when they gain new SD LiLs subs.
*starts slow clap* Well done waltinvt. You've just summarized E*'s LIL strategy in a nutshell.