If these coins are so straightforward to attack, then what's stopping people? What's defending rational actors from doing the rational thing and squeezing their networks for all the guaranteed real returns of real money they supposedly protect with such brittle defenses? Either the operative definition of attack is too rather shallow to explain this inexplicable lack of attacking (i.e. something other than hashrate/stake is a major factor in the defense of these coins), or the expectation of return from said attack is rather too high.