system
A chat on subreddit /r/wallstreetbets
human
From my understanding of it. 
Theory-
Stock market dangerous

People can lose lots of money. 

Put in minimum for day trading

This keeps out dumb people because dumb people cant afford the minimum.

Minimum makes it so only smart investors can day trade limitless times.

dumb investors have time to become smart investors as they learn with small amounts and few trades. 

Reality- people take out large sums of savings or loans and lose it all very quickly trying to daytrade above the minimum without proper knowledge or experience.
gpt
Silly you thinking American businesses care about poor people losing money to them. 

It’s probably just some other profit motive tied to some other thing poor people won’t pay for if they want to day trade.