Is beginning to pray due to approaching exams, after a six-month cessation, considered hypocrisy or an act for personal gain?

Your prayers during exam days are better than abandoning them, and your turning back to Allah during these days is a sign of goodness within you. So, take advantage of this and maintain your prayers, do not abandon them. Know that abandoning even one prayer is one of the greatest sins, and it is expected of you that you will continue to maintain them after the exams.