One of the most common goals in bodybuilding is to have big arms. Thus, the direct work of the biceps and triceps is mandatory to take arms but also to prevent injuries and improve performance.
However, getting up to speed in the room is not always enough to take arms and although you train regularly, a problem remains your arms are still not big enough. In addition to those who do not work well, many avoid working directly for absurd reasons. If you want to have big arms you have to train them directly, intelligently (with a goal of progression and good technique) and probably more frequently than you do now.
If you want to have big arms, increase the volume and training frequency of your arms up to four times a week. Higher frequency allows for greater training volume and better stimulation as shown by the Fitness Buddy App.