Being in love is dangerous for a character. Occasionally, a 'main' character who more or less pulled his weight at the start of the series starts to feel affection for another, and the writers like the idea. Suddenly, his own personal plot starts to become almost exclusively about that, and we have nothing to balance out the inherent goofiness and clumsiness that occurs dealing with his emotions. This has an extra layer of trouble if the demographic of the viewers isn't too heavily interested in the romance, or romance in general. On the other hand, other demographics can relate.