SE is very gun shy about add-ons. The fact that many current "illegal" add-ons do things they really don't want to condone (the hunt trackers and bot programs, for example) is just a nail in the coffin.
This is bolstered by the fact that certain add-ons were a real problem in FFXI, so the "scars" are still there.
In addition, they've also stated that they don't want PC players to have an unnecessary advantage over PS3/4 players in terms of gameplay.

It's fine and dandy to explore what you want to do, but you have to understand that there ARE negatives to allowing add-ons. Plus, as mentioned in other threads, the lead developers have kind of a love-hate relationship with even DPS meters, which smells to me of personal history given we know Yoshi-P HAS played WoW and there are some disturbingly elitist attitudes towards add-ons in that game ("Oh, you don't have Omen? You can't raid with us then!")