its always going to be the law of diminishing returns.
for example, if you have one indicator that gives you a 60% success rate, any new indicator will only improve your chances by smaller increments.
there will also be the possibilities that another indicator actually keeps you out of an otherwise good trade. or, if you're waiting on a second confirming signal, you get in a few bars later, costing you pips.
the question could equally be if the excess of indicators reflects a lack of confidence in the self, (constantly seeking affirmation), or reflects the fear of loss, or the attempt to impose perceived control on an apparently wayward market.
personally, I have 2 on the lower frame, and 2 on the chart. ( not counting the fractals which show me the Highs/Lows)
my excuse is that indicators are easier to code into signals, whereas eyeballing trend is more an art.