It's a metaphor. People are trying to explain spacetime to you as though it was a thing sitting in space (which obviously it isn't) because that's all the analogies there are. What else can we compare it to except some thing? But a thing (anything, any thing) sits in spacetime, and there the analogy breaks down.
What we can compare it to, which is not misleading, is the predictions made by mathematical models, which introduce no ontological claims about the things they're modelling: that is, they tell you how spacetime works without making any claims about how it's like a rubber sheet, etc.
This whole belief that there is some cosmic fabric that exists in space is bordering on an almost religious belief. Where is the hard cold science that provides any shred of evidence in the physical existance of this cosmic fabric?
That would be all the evidence for G.R. That's kinda what makes it different from a "religious belief".
Is there any other aspect of the bleedin' obvious that you need explaining to you?