There is trading activity in the milliseconds-seconds horizon as well. I'm sure all the big HFT players participate plenty. These just wouldn't be considered MM strategies.
Your original question was why MMs have to operate at HFT horizons. MMs by definition are liquidity providers (which means high availability and high volume at competitive prices). In some cases (DMMs) they're legally obligated to do so at some well defined baseline. And in that specific context HFT speeds are required.
Your original question was why MMs have to operate at HFT horizons. MMs by definition are liquidity providers (which means high availability and high volume at competitive prices). In some cases (DMMs) they're legally obligated to do so at some well defined baseline. And in that specific context HFT speeds are required.