Because you have a poor ISP. No proper ISP should block anything (except maybe child porn, but that's a slippery slope). Change your DNS to either Google's (8.8.8.8) or OpenDNS.
If you live in a repressive country prohibiting pornography you should get a VPN. I'm satisfied with my choice of strongVPN.com
If you live in a repressive country prohibiting pornography you should get a VPN. I'm satisfied with my choice of strongVPN.com