What's the most popular religion in Essos? Obviously it's the Faith in Westeros but Essos doesn't seem keen on that, yet all their religions don't seem widespread. No one but the Dothraki worship the Great Stallion and R'hllor doesn't seem to have that great of a following either.
Thanks for the question, Anon.
I think you undersell how popular R’hllorism is in Essos. We see it practiced in the most important Free Cities:
Dany could hear the singing of the red priests as they lit their night fires and the shouts of ragged children playing games beyond the walls of the estate. (“Daenerys I”, A Game of Thrones)
In Lys, Myr, and Tyrosh:
Each has its own gods, too—although the red priesthood of R'hllor holds sway in all of them and often wields considerable power.
All this is also true of Myr, Lys, and Tyrosh, those three quarrelsome daughters whose endless feuds and struggles for dominion have so often managed to embroil the kings and knights of Westeros. (“The Free Cities: The Quarrelsome Daughters: Myr, Lys, and Tyrosh”, The World of Ice and Fire)
Many of the Old Blood of Volantis still keep the old gods of Valyria, but their faith is found primarily within the Black Walls. Without, the red god R'hllor is favored by many, especially among the slaves and freedmen of the city. The Temple of the Lord of Light in Volantis is said to be the greatest in all the world; in Remnants of the Dragonlords, Archmaester Gramyon claims that it is fully three times larger than the Great Sept of Baelor. (“The Free Cities: Volantis”, The World of Ice and Fire)
Three blocks later the street opened up before them onto a huge torchlit plaza, and there it stood. Seven save me, that’s got to be three times the size of the Great Sept of Baelor … The great plaza before them was packed almost solid. Many and more of the worshipers were wearing some scrap of red cloth pinned to their sleeves or tied around their brows. Every eye was on the high priest, save theirs. (“Tyrion VIII”, A Dance with Dragons)
The Lord of Light, red R'hllor, has a great temple on Braavos as well, for his worshippers have grown ever more numerous in the past hundred years. (“The Free Cities: Braavos”, The World of Ice and Fire)
In fact, the only Free Cities where we don’t see R’hllor are the three that were formed from religious dissension - Norvos, Lorath, and Qohor. Otherwise, R’hllor has a real presence in at least western Essos.
Now, you are right to say that many Essosi religions are, I guess, specific in their demographics, for lack of a better term. “Why” is a complicated question that has to do with the age and variety of political structures in Essos, before and after Valyria. So, I guess the best answer is, “depends on where you go”, but R’hllorism has certainly a widespread influence in at least western Essos.
The Queen Regent (NFriel)