On the use of "alleluias"

I've been asked several times about why we don't use Alleluia's at the dismissal. So I thought I'd give an answer here as well.

There are two different rubrics (or rules) that govern the use of Alleluia in worship. One set of rubrics govern the use of Alleluia in music and in all of the liturgy except for the dismissal. This rule says that we use Alleluia all the time except during the season of Lent.

The other set of rubrics covers just the dismissal and it says that we only use Alleluia in the dismissal during the period from Easter Sunday through Pentecost, but not at any other time.

Why the difference? I honestly don't know - but that's what the rules say - :)