Life
A cell with two or three live neighbours stays alive. A dead cell with exactly three becomes alive. Everything else dies or stays dead. That is the entire specification, and every part of it below is a decision somebody made.
What counts as a neighbour
Conway counts diagonals. Drop them and every pattern in the menu dies or degenerates. the gliders were never in the rule, they were in the neighbourhood.
Where the edge of the world is
A glider that leaves a walled board is gone; on a torus it comes back and collides with its own past. Neither is more natural. both are somebody's choice about what happens off-screen.
Who decided the rule
B3/S23
B3/S23 is Conway's, arrived at by hand over months of play because it sat on the edge between dying out and filling up. Try B36/S23 (HighLife, which self-replicates), or B1/S1, and watch a universe with no interesting middle.
Nothing here was inevitable
Von Neumann and Ulam were after a machine that could build a copy of itself, and the grid was a way to make that question answerable: discrete cells, discrete time, one rule applied everywhere at once. Conway's rule is a later, much smaller instance of the same setup, tuned by hand until it did something neither obviously dead nor obviously explosive.
The point of the controls above is that every one of them was set by a person before you arrived, and none of them announces itself in the output. You watch a glider cross the screen and it looks like a fact about the world. It is a fact about a neighbourhood definition.