Martin Brown writes
The first flowers are almost always male until the plant has enough
leaves to support female flowers with fruits. Just wait - you will be
up to the eyeballs in courgettes by the end of the season.

Is that the reason? I'd always assumed it was to aid cross pollination -
the pollen from the first few male flowers can only be used to pollinate
another plant. But you are undoubtedly right.
--
Kay