Given the current state of Twitter, there's any number of reasons why he wouldn't want to have an account there, choice or no.
As for the blog, it's just something he likely didn't feel like maintaining because RL got in the way. I've seen plenty of creators in both the US and JP delete their accounts when they feel like withdrawing from whatever scene they were a part of in their "stupid teen years" or simply because they just felt the need to move on and leave the past behind.
Hopefully people will keep archives around forever, because let's face it, nothing truly ever goes away on the internet.