There are quite a few ways a gaming news blog can manage to stay on top of rumors and leaks. One of these is by having insiders in a gaming company. Employees leaking insider affairs isn't new or confined to the gaming world alone.

Even government and intelligent officials leak information. A gaming blog with an insider can easily collect information and post it on its site, thereby counting it as a leak.

Some also aggregate leaks from every corner of the internet. They simply scour forums, boards, and social media to find relevant leaks and post them. Additionally, it is not rare for a gaming company to intentionally leak important details to blogs so as to gauge the hype and anticipation.

Lastly, I should mention that not all blogs are as diligent with their leaks. Some blogs, like https://www.gameressential.com/ go to extra lengths to vet their sources and verify their originality, while some just publish anything they come across.