I don't think it's fair to blame the voters. If there were influential elections that nobody was voting in, then a few hardcore members of the electorate would see the potential and be all over them.
It seems much more likely that the voters are correctly detecting that the elections are not that important, either because the parliament has insufficient influence on EU policy, or because the candidates have insufficient influence on the parliament's decisions, or because the parties are all as bad as each other.
It seems much more likely that the voters are correctly detecting that the elections are not that important, either because the parliament has insufficient influence on EU policy, or because the candidates have insufficient influence on the parliament's decisions, or because the parties are all as bad as each other.