Between Bikkurim And Maaser Sheni

The Rambam in Sefer Hamitzvot #125 says להביא ביכורים לבית הבחירה, שנאמר: "רֵאשִׁית בִּכּוּרֵי אַדְמָתְךָ" (שמות כג, יט) (שמות לד, כו).  Regarding maaaser sheni, in mitzvah #128 he says להפריש מעשר שני להיאכל לבעליו בירושלים, שנאמר: "עַשֵּׂר תְּעַשֵּׂר" (דברים יד, כב) מפי השמועה למדו שזה הוא מעשר שני. He differentiates between maaser sheni, where the mitzvah is to designate the maaser vs. bikkurim where the mitzvah isn't only to designate the fruit but also to bring it to Yerushalaim. This is further demonstrated in the Rambam's list of the mitzvot at the beginning of the laws of maaser sheni and the laws of bikkurim.  At the beginning of the Laws of Maaser Sheni he says the first mitzvah is להפריש מעשר שני.  In the beginning of the Laws of Bikkurim he says the first mitzvah is להפריש בכורים ולהעלותן במקדש.  He adds the words להעלותן במקדש.  Obviously the question is why?  Why does the Rambam add that part of  the mitzvah is to to bring the bikkurim up to Yerushalaim but regarding maaser sheni he says the mitzvah is to separate the maaser but doesn't include the aspect of bringing it to Yerushaliam. Why is there such a difference?

We see that there is a major difference between that which maaser sheni must be eaten in Yerushaliam vs. the bikkurim.  The confines of maaser sheni inside Yerushaliam are dinim on the person eating it.  It is an obligation of the person to confine the place of his eating.  The bikkurim on the other hand must be eating in Yerushaliam is a limitation because of the cheftzah, the bikkurim demand that they must be eaten only in Yerushaliaim.  Hence, maaser sheni isn't defined as something that must be brought to Yerushaliaim for that is merely an obligation on the owner.  It is bikkurim that is defined as something that must be brought to Yerushaliaim.  That is what we see.  Why that is and/ or where it comes from, I haven't much of a clue.  The suggestion box is open.