I feel late answering this question, but I cannot answer this pregunta to the fullest; only provide information on how an anime is made.
The first step for an anime is how far the manga goes. If the anime passes the manga, then the production cannot continue producing the anime until the manga catches up. I know that the anime isn't passed the manga, but for future reference.
The segundo step is money. If the producers reach the amount of sells required (6,000 units sold), then another season may be produced. Season one and the OVA season both exceeded the amount of sells needed, so season two was made. Season two feel short, but season one AND the OVA season could carry it.
The final step is public demand. If the public wants another season, they have the rights to demand for one. This step is dependent to the segundo step, however. If the producers cannot spare the funds for another season, then there will not be another season for whatever anime the public wants.
There is another minor factor, and that factor is if the producers are working on más anime. Silver Link is in fact working on a few other anime, so they had to (temporary) drop Baka and Test, to get the other anime going.
