the plumbing of the us stock market like actual plumbing tends to operate quietly in the background in january as if a wall had been ripped open the market’s tangled and decadesold pipes were suddenly exposed to millions of retail investors who had given little thought to them before they had piled into stocks like gamestop ticker gme then at the height of the mania some brokers including robinhood markets hood whose explosive growth has been fueled by new investors restricted trading in those stocks