IMO they have mandated it at pro level in order to protect themselves as a governing body I suspect, its best to be seen as pro-active is getting players to wear the new models that have been designed and invested in by the helmet manufacturers than be reactive should such a tragic incident as the Phil Hughes scenario every occur again from someone being hit in the helmet itself.
From the helmet manufacturer side its not a cheap exercise to have to go through in order to test the helmets to the new regs in terms of product being submitted as well as the actual cost of the testing itself, not even accounting for the design hours, CAD costs, tooling costs and multiple other factors that have had to be spent out in order to get to the stage where a certificate can be granted for compliance. But as the BSI committee identified improvement was needed we all undertook the task of improving the levels of protection provided in order to meet the standard.
@Kevtheplumber not sure why you have to buy a new helmet each year as 2013 complaint helmets were available to purchase at the start of last season?