Maybe by the time a civilization achieves the tech needed to really expand, they no longer want to.
Is that your candidate for the Great Filter?
There's just no way every commoner gets their own Caribbean cabin. Unless we find some unlikely physics hack in the last few vestiges of scientific unknowns, any interstellar travel seems impossibly difficult.
An alternative future: we live forever as brains in the vats, plugged into infinite virtual worlds devoid of scarcity, life-threatening danger or physical constraints. Most of the human activity takes place there, with occasional interactions between the virtual and the real. No new physics required, just a series of incremental improvements in biology and computing.
A stable future can plausibly take many forms, not all of them are nice.