To be honest they inherited all these applets (and applets-only) security exploits from Sun. Sun are the ones to blame here.
Actually the ones to blame are the uber f^^^tards who thought that Java applets was a technology worth anything.
One should go back in time and read Usenet's comp.lang.java.programmer from back in the early Java days. There were two camps: the retards who thought applets were a good idea and going to revolutionize the Web and the enlighted ones who pointed out that it was all wasted energy on a piece of shitty technology that would only create problems.
I was in that latter camp and, honestly, it feels good to see that no-one is disputing anymore that Java applets were really one of the most f^^^tarded piece of technology ever invented.