Dumb canon question: How did Mobile Armor become the standard over MBTs like the Type 61?

I have been checking the various wikis, but I can't find a concrete answer.I mean, of course the Armor and Suits are cooler so it'd make sense to just gloss over tanks in the early days, but there certainly would have been an explanation somewhere in there. Especially since even a simple Mobile Armor would be hella expensive compared to even a full squadron of tanks.