I think a lot of botnet operators are also worried about their bots being "discovered" during sustained bandwidth attacks. Your average home user isn't going to

I think a lot of botnet operators are also worried about their bots being "discovered" during sustained bandwidth attacks. Your average home user isn't going to notice their internet being weirdly slow for a couple of hours every few weeks, but a sustained DDoS will have people noticing and potentially discovering / cleaning their devices. ISPs might also take notice of the sustained outbound traffic volume, identify a pattern and contact customers.