Public proxies are often managed by unknown third parties who can theoretically intercept the data passing through them.

While downloading a free list of 10,000 proxies might seem efficient, public lists often carry hidden dangers:

Many IPs in these public files are already flagged by major websites (like Google or Amazon), rendering them useless for scraping. proxifly/free-proxy-list: Free HTTP, SOCKS4 ... - GitHub

The .txt format is the industry standard because it is easily "parseable," meaning software can quickly read and rotate through the list without complex processing. Primary Use Cases for Large Proxy Lists