The problem is that MSZP have basically collapsed as an organized entity... iirc polls have them behind or level with Jobbik.
Last Election
Opinion Poll
Is it due to Fidesz' policies, or did they just kill themselves ?
Self-suicide and economic crash of 2008 (which hit Hungary very hard). Plus as Al pointed out the MSZP is a "post-communist" party and so has all the baggage that goes with that and as post-1989 East European politics has shown, ex-commie parties even reformed as the most neo-liberal social democrat, can fall pretty hard if things go wrong.
@Belgiansocialist: Have you seen post about the "art of the new constitution"... that says everything really.