spread traders provide the liquidity to speculators. and act as market makers
for small size accounts, spread trading the reward is too low for the time and work doing the trade.
your account size or capital needs to be large to make it worth the capital as returns are lower if you spread trade. that is why some traders don't bother with spread trading.
Also some contracts are too illiquid to trade especially the options in futures
there is no bid or ask in the options.
I keep reading comments about small account size and large account size. Can anyone here define what constitutes a small account and what constitutes a large account?