Nobody manages those numbers by themselves. If they do they really manage like Randy only the 5-10 sites that actually produce anything. I know this because I do the same

. Only really manage my 5-20 sites where 5 get all the attention and the other 15 get minor attention, then everything else gets no attention.
I also have a high number of domains and sites, but most are abandoned projects or once good now bad sites.
I turned many of my abandoned domains to those parked pages and make some money on that every month. Its not a lot, but its better than nothing. Its the same formula the domain hoarders use, but on mass scale.