The standard model largely comprises of four fundamental forces (electromagnetism, gravity, strong, and weak), but beyond these models no further explanation exists. Then, what is a "force"? What compels the particles to behave in such a way that they do? We often just tautologically and empirically accept the fact that forces exist. Such is not a satisfactory answer, and there must be an underlying elegant and consistent mechanism that allows forces to exist.
String theory and concepts like multidimensional manifold confinement kind of cheat the model and convolutedly bypass the pitfalls by adding more and more complexity to the model, trying to explain away the discrepancies by adding more assumptions. However, fundamental driving mechanisms of nature is rarely this complex; the added complexity is costly to reproduce and pervade, and thus not expected to be as universal as the medium of spacetime.
Then, since we are indeed dealing with metaphysics with eons away to have some relevant experimental data, what is the alternative simple model that can elegantly explain the origin of the forces of all kinds? Maybe the hint lies in us; it is somewhat insane to insinuate that biology can be infused with metaphysics (and you may think; "how anthropocentric"), however there exist a shared fundamental cry of all living things that is universal: all life want to live and flourish. It is a simple concept that ultimately drives all living beings; to continue, to live on, to survive, to endure at all cost, to never give up, and to eventually thrive, flourish, and conquer.
There is dynamic power behind this drive that is shared by all life. Even though the scope of biology is a few tiers higher than metaphysics, this can serve beautifully as the source of the feedback cycles of fundamental drive of forces; the same force that make particles resist its inertia and move toward something else; as if it is compelled to move away; as if the particle behaves like it wants to survive, sensing and veering toward spacetime with better concluded chance of continued existence.
For us earth-bound humans, spacetime may feel hopelessly vast. However, as with all living beings, we will do anything to ensure our survival, which would mean in the foreseeable future, we will likely venture out into the vastness of space to further guarantee our survival, busily gathering more far away resources and optimizing further to live on and flourish, beyond this galaxy, beyond our local group, continuing to expand outward toward the unending edges of the known universe, never stopping until we have fully crystalized the known universe (e.g. our knowing anti-matter to be a great source of energy, we will always force our hardest to reach sections of the universe that is constituted entirely of anti-matter, thus simulating ⊕⊖ attraction model, observable in electromagnetic interaction), This bustling "business" or "activity" is the mediating and carrier mechanism of the forces within the universe and likely what determines how our universe will behave as a unit: a particle.
However, this is all just theoretical and speculative.
A fleeting dream, of a nap under a tree on a nice Spring day.