Markets are reactionary and thus too slow.
Example: there were no laws preventing diluting stock during a hostile takeover until after Vanderbilt tried buying out the Erie Railroad and diluting stock was a way to swindle him [1]
[1] https://en.m.wikipedia.org/wiki/Erie_War#Watered-down_stocks
They react to different types things. Both types are important, which is why we need markets as well as some amount of regulation.