I’d say that being mentally unwell is absolutely part of it, but leaving it at that is too simple of an explantion.

Based on what I have read it seems like the complete disillusionment he experienced with the country he worked to defend, combined with other external factors possibly lead to a manic episode where he saw no other way to try and stop it which lead to this tragedy.

Just handwaving it away saying

Because he was mentally unwell? Big shock

get you no closer to understanding and preventing incidents like this in the future.

You are treating him as if he lived in a vacuum and there are no other parties that affected him.

Not saying I support it but there’s a long tradition of self immolation as protest. It’s not accurate to blame it all on mental health