The sugya currently under discussion is that of “Chullin She’Naasu Al Taharas Hakodesh”, ordinary non-sacrificial food that is prepared and eaten with the strict guidelines of Kodoshim.
Why would anyone want to impose those complex rules upon himself?
Rashi offers an explanation at the bottom of 19B. He suggests that there are people who frequently eat Kodshim and wish to remain in the habit so that their families will be careful to maintain the Taharah required to eat Korbanos.
I can understand that Kohanim would wish to maintain this standard. Why would people outside of Yerushalayim or after the Churban want to keep these rules, which are elective?
Furthermore, why would the Chachamim ratify this chumrah by giving it halachic parameters?
There is much history that must go into answering all these questions. Other issues that need to be addressed is how such a massive sub-stratum of society as the “Am Ha’Aretz” group came to be. These people were ostensibly observant in all other respects of halacha except for Maaser and Taharah. This division between Chaveirim, those who were knowledgeable in the laws of Taharah, and Amei Haaretz who were not, must have been jarring. Imagine a group of Jews who refuse to come anywhere near other Jews. This goes beyond not accepting certain hechsheirim, which is the closest modern manifestation of the Perushim-Am Haaretz divide.