When I read "Hero leaves the weapon behind", I thought you were going to reference Deadpool leaving the bag of guns in the taxi. In that case, it was because the final showdown in the script was supposed to be a much bigger event, but the studio cut the budget by a huge chunk, so that final showdown had to be cut down significantly. Deadpool leaving all the guns behind was a nod to that change in the script.

Instead of an annoying trope, it's a pretty funny moment.