Mostly because the majority thinks Core makes generally good changes. If most people agreed that someone else has made a better change, they'd use that instead.
that has nothing to do with the argument. but re your point that simply is not true either. core was simply never challenged before. all protocol developers simply contributed to core. the rift only happened due to the block size debate. all the past conflicts were about what to put in core and not to launch a competing implementation.
we are in uncharted territories here and I for one hope core's monopoly over the Eco-system is broken. we'll all be better for it
