Avant tout vs D'abord

Why is 'Avant tout' used as the translation for 'First of all', and not 'D’abord' – which is not given even as an alternative.  I understand that d’abord indicates a sequence – first before other items – while avant tout is more like above all – a priority or emphasis, but not necessarily sequentially first. So I would have thought d’abord was more appropriate here. Or is this a deliberate use of the term to show that the person really means 'above all'. A distinction that 'First of all' doesn't really imply in English.