We need the help of experts to interpret the world for us. Earlier, those interpretations and world views were available via books. This introduced a serious time lag from “thought to publish.” With blogs the their “thought to publish” cycle is reduced to minutes rather than months or years.
Yes, this is one reason but it’s already good enough I guess.
Note: While you can’t ignore blogs, who you chose to read is equally important. Check your RSS subscriptions. Should you include someone else? Should you drop someone?