The actual reason is to make money of course, everything anyone else says is lies, FUD and disinfo

quark took this to the extreme and it made them millions in less than half a year.

doge went for this + meme but they made the block halving longer but still short.  because it takes ~2.5 minutes they keep getting hit by multipools

reward halving guarantees you can mine early and have something vastly more scarce to mine later, meaning if people want it, they have to buy it (from you)