Routers, esp home routers are also a horror story, esp. with scumbag vendors EOLing devices and not patching vulns for devices that are still running on the internet.
Still, if you look at Mirai, it’s not primarily infecting routers. It’s mostly cameras, DVRs, & printers.
Expecting end users to deploy network appliances with strong network security policies is a lost cause, and this stuff is just going to get worse. Mirai was amateur hour grabbing low hanging fruit. Trying to put in the public eye that hundreds of thousands of IoT devices are doing really bad things because some manufacturers suck ass is important.