There are a number of LCCs (although I would use the term "low cost" advisedly these days
) that do provide seat allocation, TUIfly, Air Berlin, Flybe to name just a few in Europe. I may be wrong, but I think Germanwings have introduced it too. The argument used by RYR and EZY is that free-for-all seating expedites the boarding process and enables them to meet their short turnaround times. This might be true when using front and rear exits on remote stands, but not when using a single airbridge. For me the most efficient system (when using an an airbridge) is seat allocation with boarding by row number groups, starting from the rear. I experienced this with Westjet in Canada and it worked well - thanks to organised ground staff and disciplined passengers!