Another likely source is "free" VPN tools, or tools for streaming TV (especially football or other pay-to-view stuff). The tool can make a little money proxying

Another likely source is "free" VPN tools, or tools for streaming TV (especially football or other pay-to-view stuff). The tool can make a little money proxying requests at the same time. I can't provide evidence as it's close to impossible to separate the AI bots using residential proxies from actual users, and their IPs are considered personal data. But as the other reply shows, it's easy enough to find people selling this service.