There are only two brachos that we are Biblically obligated to say: birkas hamazon and birkas haTorah. The gemara even has a hava amina that we can derive the obligation of one from the other: if one must recite a bracha on material food, certainly we must recite a bracha on Torah which gives us spiritual sustenance. While such a hava amina perhaps points to a relationship between the two brachos, nonetheless there is a clear difference between them: birkas hamazon is recited after eating, while birkas haTorah is recited before learning. Why the distinction? The Sefer haChinuch explains that birkas hamazon gives thanks for a physical good; the physical enjoyment and pleasure from food comes only after it is consumed . Birkas haTorah gives thanks for an intellectual and spiritual good. Even before one beings to learn, the mind can appreciate and anticipate the joy of being engaged in studying the dvar Hashem.
The gemara tells us that one of the causes of the churban was that "lo beirchu baTorah techila," the Jewish people failed to recite a birkas haTorah before learning. R' Altusky, the Rosh Kollel of Darkei Torah in Far Rockaway, in a derasha on Tisha b'Av cited the Sefer haMakneh which notes that the gemara does not say birkas haTorah was omitted, but rather says it was not recited "techila", before learning. There was a lack of anticipation for learning, a loss of the distinction between material pleasure which is enjoyed after the fact and spiritual pleasure which must be yearned for and appreciated before one even begins the process of study.