Because the average person is familiar with religious tenets, but not so much for philosophy. And philosophers have a reputation , right or wrong, for sitting under a tree with other philosophers discussing issues but not producing anything of value, they 'don't work for a living'.
But philosophers have to know a little about everything, and they are among those with the highest IQ's. Socrates said that philopshers should rule nations, because they are logical and would rule fairly , unlike politicians.