Because it is meaningless crap and leads to less educated pilots thinking they have some form of seperation when they don't.
It also means those of us that are going to ignore such meanless crap have to listen to it before deciding its meaningless crap.
Then muttering under our breaths "whoopty do"
Its in the same league as "your on guard" when folk are doing practise pans.
And similar to 500's experence all the TCAS units I have used give way more errors than 30 degs especially with none mode S contacts. The contacts jump from left to right sides on the screen and also forwards and backwards. The slower the traffic the more error there seems to be calculating what it is doing.
More to the fact you have been given traffic which you think you have on your screen you declare it. That traffic thinks everything is fine. Actually unless that traffic has been asked you don't have a clue if it has its transponder turned on, your contact could very well be something else. That none transpondered aircraft could then change level with out saying anything and your still looking for that other traffic which is actually on another frequency.