Why? Because the Episcopal Church (in the United States) is governed by a legislative body and a constitution. It is a democracy.
You can blame the founding fathers and the American revolution, probably. Though not written by the same people as the U.S. Constitution (as is commonly held) the men who first wrote the Constitution and Canons of The Episcopal Church desired to
replace hierarchical rule with egalitarian, democratic government (1)
Here is Article I, Section I of the aforementioned Constitution (emphases mine):
There shall be a General Convention of this Church, consisting of the
House of Bishops and the House of Deputies, which Houses shall sit and
deliberate separately; and in all deliberations freedom of debate
shall be allowed. Either House may originate and propose legislation,
and all acts of the Convention shall be adopted and be authenticated
by both Houses
Though probably not as much a "matter of faith and morals" than it is simple democratic governance, the General Convention is
likely as much guided by the Holy Spirit as is the Pope.
EDIT: As concerns comment toward the word "likely" and to further improve this answer in response to improving the question, here's this from the House of Deputies.
Deputies and bishops cannot be instructed to vote one way or another
by their diocese. They agree to come to Convention with an open heart
so that they can prayerfully listen to others and be led by the Holy
Spirit. And, they cannot refuse to vote on an issue.
And this, from The Anglican Understanding of the Church: An Introduction by Paul Avi. (The Episcopal Church is part of the Anglican Communion.)
Anglicans maintain that the doctrine, worship, ministry, sacraments
and government of their Churches are those of the Church of Christ and
that they are owned and blessed by the Holy Spirit.
And this delightful passage from The Journal of the 38th Annual Convention of the Protestant Episcopal Church of the Diocese of Southern Ohio (1912)
And now, with all my confidence in your right-mindedness as a body, I
still feel bound to remind you at least of the spirit in which you
ought to enter into such an election, of the utter conscientiousness,
of the utter independence of judgment and action, and of the utter
dependence upon the leading of the Holy Spirit with which you ought to
And, you know, we're Christians. We trust God. We pray all the time. For guidance, strength and wisdom. Especially when making tough decisions.
God has made a promise to us:
I will instruct you and teach you in the way you should go; I will
counsel you with My eye upon you (Psalm 32:8)