Some people want to be contacted regularly by Home and/or Visiting Teachers, and they get upset that people don't visit enough; other people are more independent, want to be left alone and get upset that people keep trying to visit them. The "proper" solution varies by individual (to visit or not visit - and how often to visit), but that's almost impossible to analyze quickly, so the "easy" way is to lump everyone together into one category - the "must-be-visited-exactly-once-a-month group".
The proper solution, ironically, already exists in the Church - Personal Priesthood Interviews (PPI's) and the Relief Society version. (I prefer "Personal Stewardship Interviews" - since that term can apply to anyone, male or female.) When done correctly, they don't focus on numbers but rather actual people - and HT and VT can be adjusted and adapted accordingly.
That's just much harder to do than focusing on the numbers.