This blog post mentions parking an old switch with a derpy little raspberry pi.
Also, what makes colocation something for businesses is cost. The likes of Hetzner also sells colocation, and nowadays you can buy a used rack for around $100.
Moreover, today's COTS computers are not like your parent's. A mini PC selling nowadays for peanuts has gigabit Ethernet, 16GB of RAM and half a dozen or so cores. You'd pay a small fortune for servers with those characteristics in the early 2000s, and nowadays that hardware is used to check emails.