Amoroim and Kavana in Tefillah

Here is a fascinating Gemorah found in Yerushalmi Brachos at the end of Perek 2 Halacha 4 (Daf 17b at the bottom of the page.) A simple reading of the gemorah comes out that these Amoroim are saying that they didn't have kavana when davening! How could it be? What does this Gemorah mean? What is it coming to teach us? What can we take from it?

א"ר חייא רובא אנא מן יומי לא כוונית אלא חד זמן בעי מכוונה והרהרית בלבי ואמרית מאן עליל קומי מלכא קדמי ארקבסה אי ריש גלותא

שמואל אמר אנא מנית אפרוחיא

רבי בון בר חייא אמר אנא מנית דימוסיא

א"ר מתניה אנא מחזק טיבו לראשי דכד מטי מודים הוא כרע מגרמיה

Granted that the Pnei Moshe explains by all these Amoroim the problem was is that they were thinking in learning (and for that reason weren't m'kavain in their tefillah.) Could be there are other mafarshim, tzrich l'ayin. With this pashut it certainly comes to answer a little bit. Obviously one would say our lack of ability to be m'kavain in Tefillah has nothing to do with the fact that we are so "tored" in our learning. Again, tzrich inyun into the whole thing. None the less a very interesting Gemorah.