Because the mortgage deduction gives individuals too much control over their own lives. "Targeted" means top-down government control.
All governments aspire to be the Soviet Union if you let them.
I'd say that actually being forced to deal with government spending would induce individuals to reassert control over government spending by electing representatives who were more mindful of the link between government spending and revenue.
You know, kind of like we do at the Federal level.
(Ha ha ouch.)