Because I don't think he has any intention to sell it at all. This thread kinda prove it, he offered the account, then faked an escrow to steal the fund. He'll gain extra fund and never have to part with the hero account. Maybe it's not the first time he's done this, given the screenshot was made in April, never have guessed someone will sacrifice their account to be tagged as account buyer to report his scam attempt.
I noticed something strange in the picture the OP posted that the scammer sent him, I mean look at the authenticity of those screenshots carefully. The scammer seems to have succeeded in deceiving the OP by falsifying the account identity by editing the image without paying attention to small things such as the vertical layout of profile information. If you are confused about what I mean, then look at the image once again. So I think it's possible that OP was scammed by someone who didn't actually have an account to sell. Fraudsters get another user's account at random and fake their image. I'm not completely sure about that, but it's a possibility when I noticed the screenshot of the account the scammer offered him.
Here's the comparison: