Now being an initiate is not the only way to worship a deity. Initiates of associated deities also can worship the associated deity and sometimes even get a Rune spell for it.
And of course don’t forget lay members. It is usually easy to become a lay member, and for that you can get training, spirit magic, and some level cult of support. In many cults, most people are lay members.
So in Sartar, 34% of the adults are initiates of Orlanth, but another 50% give or take are members of Orlanth’s associated cults. And a few more percent are lay members of Orlanth.
Or how about Humakt? Only 3% are initiates of his cult, but as much as another 3-4% are lay members!
Less than 1% of the adults are initiates of Odayla, but another 38% belong to cults associated with Odayla. I suspect far more people worship Odayla through the Orlanth cult than directly.
If I am an Orlanth initiate, no reason not to draw on this associated cults as well, and become a lay member of Humakt or whoever else might be useful.