Because cable QOS sucks. Both technical QOS and service from the vendor. I have a 16Mb connection right now through TWC/Spectrum. In the last year, it's gone out at least 15 times, usually during primetime. My upload speed is horrible, roughly 1.5mbps. In my town, a new fiber vendor is bringing FTTH, charging $65 for 100mb/sec, and $100 for gigE. This is symmetrical too, and upload speeds are important for good offsite backups etc. My vendor allows self-hosting, basically with the statement that as long as you're not doing anything illegal, you can use the pipe as you see fit. Try running an smtp host on TWC or the other bigCo vendors.