[Avodah] The relevance of shmitta nowadays

[Goldmeier]

In my shiur tonight started learning Siman 67 of Choshen Mishpat which 
discusses the halachos of shmittas ksafim. In se'if 1 the main topic of 
discussion is whether it is at all relevant nowadays m'd'rabanan.

Very interestingly, in the SMA seif kattan 2, he says that this 
discussion of shmittas ksafim being nogei'a today as a drabanan is only 
regarding shmittas ksafim, but not shmitta of charisha and zriya. He 
then gives two reasons why the chachomim never made a takana that we 
have to refrain from planting during shmitta nowadays - 1. because it is 
a gzeira nobody would listen to, as when shmitta is drabanan there is no 
bracha of shana shishis (he says the bracha only applies when shmitta is 
mdoraisa) so if they couldnt plant they would have nothing to eat. So 
chachomim did not make a takana against planting because nobody would 
have listened. 2. because it wasnt relevant to make a takana in chu"l 
because there is no kedusha there, so they didnt bother making the 
takana in Eretz Yisrael either. (whereas regarding shmittas ksafim, they 
made the takana for everywhere including chu"l)

Am I misunderstanding something? In all the arguments over shmitta 
nowadays, I never heard that we dont have to keep it at all because the 
chachomim never made the takana. And if the chachomim really did not 
make a takana to refrain from planting "nowadays", did they make a 
takana later, or why do we keep it at all? If they really never made a 
takana, so why are we so machmir and fight about hetter mechira - we 
dont have to keep any of it!It is not even a mitzva d'rabanan to keep, 
if the SM'A is correct that there was never a takanas chachomim!

Kol tuv
Rafi Goldmeier