I'm surprised by the arguments wanting to place blame for this largely/solely on the security guards. These "security guards" are very much mislabelled and are the people you see standing around in a "security" vest with a large bunch of keys on their belt in your local shopping centre and they know, under current law, they have no power to detain, search or touch anybody. At best all they can do is insist verbally that you follow the rules, but if you wanted to leave the "quarantine" building that had literally no power to stop you.
Secondly they didn't know the rules or even understand what they were doing there or just how important there job was. It is now well understood they were hired with less than a days notice, provided little to no training or guidance of substance and were working for or below minimum wage. If I were in there shoes I'd be pretty chuffed if I got paid cash in hand and got a root out of it as well, for a job that would last just a week or two before I went back onto Jobseeker.
I believe all other states took up the offer of bringing in the police/defence force to provide strict quarantine measures and have not had the cluster fuck that has befallen Victoria.
So yes, at the end of the day the buck falls squarely with the Victorian State government. They did not deal with the quarantine correctly and continue to make huge mistakes, like telling people who have been tested they don't have to quarantine unless they have symptoms. They are the reason Australia is now at risk of a second wave and Andrews should immediately resign and allow someone with some level of competence take over and hopefully start to reign this in.
At the end of the day Victoria would have no community transmission if not for the governments quarantine failures. Every other state has fuckwits that would have willingly spread it to everyone if they had been allowed to catch it, but competent state government action prevented this from occuring.