They don't provide any utility either so nobody cares if the coin is insecure or its blockchain mutable, they care about how much pump and dump is going to happen.
While this is often true for altcoins, this has nothing to do with their vulnerability to a 51% attack.
I was pointing out the fact the reason why there sometimes isn't any market reaction to such attacks and why people don't care. But it kind of has a lot to do with 51% attacks, lack of utility means lack of interest hence lower price which translates into low profit in mining it hence lower hashrate which is the reason for vulnerability to such attacks.
If they were useful, they would have had higher price and more miners and higher hashrate which would have made the attack a lot harder.
Another major reason is the incompetency of their developers. As you pointed out majority of them are copy coins and those who copy another project have very little understanding of what a 51% attack is let alone be capable of thinking about solutions.