Car tax payment system not fair on less well-off

The tax disc for a 1600cc car (registered before July 2008) costs €544 for a full year, €301 for six months (which would come to €602 for a full year), and €153 for three months (which would come to €612 for a full year).

The main reason why people would tax their car for the shorter periods is that they can’t afford the tax for a whole year.

Has it never occurred to anybody to ask why the people with the least money end up paying the most?