It's more of a psychological rationale rather than a logical one. My biggest pet peeve in trading is buying something and watching it sit there. I rather give up some upside from explosive up-moves and make steady profits when we are rangebound and go up slowly (or even if it drops slightly). Recently I tried buying the shares outright since I was extremely bullish, but the whole time I just felt completely uncomfortable and not confident.
In the future, when I'm very bullish, I may test out buying shares and selling more calls during rallies (20% of my position per selling trigger instead of my current 10%), but we will see. For now, I'm much more comfortable selling puts in general and letting my bullishness dictate position sizing rather than selling puts/buying the underlying.
