A person who buys a Tesla has no idea how any of it works, but if someone breaks into that car and drives it (non-autonomously) into pedestrians how would I be held liable for that? I wouldn't be and shouldn't be. The person who broke into the car and drove it would be, the difference here is that the perpetrator is harder to catch so people look to blame something else.
At the end of the day it is very difficult to impose security management across consumers. You cannot expect the average consumer to pen test their home network and have active vulnerability scanning software to mitigate potential vulnerabilities that result in Botnets.
It is difficult to hold people liable when someone else misappropriates their assets in a way that was not its original intended purpose. When its difficult to capture the perpetrator people start to blame everything else, that doesn't mean we should just shift liability to the buyer who is just simply an easier target to place the blame on than a random unidentified person in another country.
That may sound like a solution but its not the right one. Now someone has the ability to misappropriate your assets from the other side of the world and you become charged with the crime, when all you did was buy a new Samsung TV. Heck knowing that, maybe someone would target you knowing full well you'd be in trouble for it.
Look at the moment, the owner of devices that participate in DDoSes are not head liable, and neither are manufacturers who don't secure their shit.
This needs to change.