For me it is because that is how my mind is wired for relevant focal lengths considering whatever I am trying to shoot at any given time. Crop factors tend to bug me nowadays. I messed with a lot of film before I had a digital camera so I learned appropriate focal lengths for various situations that way.
I would like to add a thought to this...this is another huge misconception perpetuated on the net imo. No one format is inherently better than any other. It is more about form, function, and application. Brand A is better than brand B is another thing like this.