Because of mandarin's lack of stomach and high metabolism, it has nothing to do advances or animal husbandry, unless you are someone that cultures pods and doses regularly.
They may be able to be kept in a smaller tank, but is it practical for most to do so is the real issue.
It can take a while for them to starve out, so typically we see these "it can be done" bandwagoners promoting doing this, yet rarely do those people stand up and admit their mandarin starved out eventually.
For those of us that have been in the hobby for long enough to know better, it's a frustrating endless cycle to see people continue to advocate keeping them in tanks that will not accomidate their needs.