Probably because they follow in the footsteps of the male celibate Jesus Christ.

Jesus, a devout Jew, no doubt held to the Jewish belief that the command to procreate and populate the earth was binding, since his Father had commanded it.

Thus it precedes your whipping boy of a " male, celibate Roman Catholic hierarchy".

Once you get the Father to endorse your morality of "if you have a flagpole, it needs to be saluted", you'll be cooking with gas.

Until then, it is all just gas.