Dude, you weren't discussing one specific individual...

After years of reading through 5e forums I became exhausted with its mother-may-I BS where everything needed to be codified in the rules in order to exist in the game.

The question here is, why make a character around a theme or a concept if the game mechanics in no way reflect your character's theme or concept? For example, if you want a character to be a nimble, quick witted, swashbuckler but the game mechanics don't distinguish between a nimble fighter and a tank.

The reason you don't understand is because you refuse to.  You have rejected out of hand the most probable reason for this.  The idea that wargamers feel that "mimicry of reality is ultimately aside from [the enjoyable] experience" is belied by many of the documents of the time.  Not only did wargames develop as a military tool specifically to realistically simulate military engagements, but also many of the players are doing so as a speculative exercise, dependent on the realism of the game.  The same people who wargame are the same people who argue about what would have happened had Pickett not charged, and they want their game to help represent those outcomes.

I think the best context to understand the nuance here is with a parallel argument;

"If one likes to salt their food, wouldn't the logical conclusion be to simply have a Salt Lick?"

Anyone who has ever houseruled is guilty of "ignor[ing] them or ma[king] up your own."  It's about what the rules are meant to represent and what you are trying to do with them.  I would argue, because the rules evolved from wargaming, that the original intent of the rules were to simulate reality, and that they rules grew and changed to simulate a particular fantasy "reality."  If you approach the rules as attempts to quantify the possible outcomes of a real problem, then no one ruleset is going to be able to effectively simulate those outcomes.  You will constantly have edge cases and "unrealistic" results from your rules that you will need to ignore or develop secondary mechanisms to handle.  Hence the "rulings, not rules" mentality you hear associated with "old school" gaming.

So it's easy to understand why gamers who grew up viewing their rulesets as attempts to guide them through the resolution of "reality-based" situations would prefer systems where incompleteness and inadequacy are base assumptions of the ruleset.