Hiroshi Yamauchi, the grandson of Nintendo's founder Fusajiro Yamauchi and president from 1949 to 2002. His childhood and adolescence was evidently plagued with a tense and stormy family relationship, which characterized many of his actions as president. It's very much worth noting that many of Nintendo's leaders entered the company during Yamauchi's tenure: Miyamoto, Iwata, Yokoi, Sakurai, Furukawa etc. Yamauchi personally made sure to hire Yokoi and Miyamoto, IIRC.
He's not the sole reason why Nintendo's anal about financial expenses (including unions) etc. But as one of the main forces behind Nintendo's transition from cards to video games, he was personally behind the idea of structuring Nintendo's working conditions around contractors instead of labor unions and maintaining as little expenses as feasible. Also, Hiroshi had a - by all accounts - very strong interest in securing his own powerbase to say the least.
As for why they still carry on, it's not just sheer inertia, but also the fact that Nintendo saw its major expansion under Hiroshi. "If it ain't broke, don't fix it" logic. One of Hiroshi's positive aspects was that he was very good at incentivizing his workers -
he spurred Yokoi, Miyamoto and others to always come up with new ideas. That's not to say there weren't misfires during Hiroshi's term - there absolutely were, from the love hotels to the Virtual Boy - but he was a major presence regardless, and it's evident in how Miyamoto still carries that kind of thinking.