Well being tall is the smart as having a bigger penis in the eyes of women. To be honest I don't know whether tall men with average or below average looks get women hitting on them. Maybe there are some tall men on the Coli that can illuminate us as to whether women hit on them and how frequently. That said, to answer your initial question, if women don't approach you, it is most likely you lack whatever tangibles women necessitate as being worthy of approach. To flip the statement, men don't approach women whom lack the tangibles we find attractive, like beauty, breast size, body, etc.
Most likely you lack the body or appearance. But fear not: I don't get hit on by women either and neither do most men (60% or more).