I don’t know what you’d consider “sizable” but a lot of people these days are spiritual without being religious. Which is unsurprising. Atheism/agnosticism are on the rise, so it makes sense that people who believe in a god but don’t subscribe to a particular religion are also on the rise.
You’re assuming belief in the Abrahamic God to make your argument easier. But not all theists subscribe to such a position. And belief in a disinterested god who created the universe seems just as plausible as believing in a disinterested programmer who wrote a simulation.