Atlan was now all alone by himself, with nothing but the Remedium by his side.
Anyone would have trouble with blowing themselves up. After all, it was in a human's self-preservation instincts to always protect oneself. Even if they were told that they should do it because it was the right thing, they would still have trouble letting go of that last protection they had of themselves.
It was like telling someone to hold their breaths for a long time until they passed out into unconsciousness. Even if they tried their hardest, anyone would heave for a breath as soon as things got too tough. They wouldn't be able to make themselves unconscious.
But there was one person who could do that. That was Atlan. This was the reason why he was able to impress the God of Death in the first place and inherited all his powers. If he didn't have that decisiveness to do the things that needed to be done, then he wouldn't have jumped into the God of Death's maws.