In the Great Middle Way, the translation of “Tathagata” is given as “One Come (Back) Thus”, rather than “One Gone Thus (to Peace)”. The original Sanskrit supports both translations —it is not whimsical.
Some schools of Dharma (in particular, those concerned mostly with individual liberation) may be less interested in exploring and promoting an understanding of karma and rebirth than those whose primary concern is universal enlightenment, which requires the willingness to return to cyclic existence to assist suffering sentient beings to attain liberation and enlightenment.
If there is no re-birth, then the suffering of a lifetime is neither beginningless nor prolonged, but rather a fairly circumscribed and quite momentary experience, requiring no greater exertion than resigned endurance for a few decades. Death would bring a happy ending to all sorrows; why trouble ourselves with any further practice?
If there is no re-birth, then the teachings on karma are false, as most often a sentient being does not —in one brief lifetime— experience the full result of his/her actions. No re-birth = no karma.
If there is no re-birth, it would follow logically that death will end all suffering. Why, then, would the Buddha teach the Middle Way? Why not just promote mass suicide? And, if we are concerned for the suffering of others, why not just kill them all? Obviously, these ‘solutions’ to suffering are distinctly proscribed in the Dharma.
It is the thought of interminable suffering (our own and that of others) that spurs us to arouse the heart of compassion, bodhicitta. Thus, the schools of Dharma that cultivate bodhicitta are certainly concerned with rebirth, and the great spiritual Heroes, the Bodhisattvas, are the models whom we emulate.
May all be free from suffering and the causes of suffering!