Because each type of object can be enchanted only with certain types of enchantments. A Ki Focus is not a weapon, so it doesn't qualify in the rules to have any of those enchantments put on it. But the rules, it can't be enchanted with anything at all(since it is not a weapon, not a wand, not a staff, not an orb, and so on and each of those enchantments needs to be put on the appropriate type).
You need a table saying "+1 Magic Ki Focus costs X". You need a bunch of enchantments that say "This can by put on Ki Focuses". Otherwise you can't enchant them at all. Yes, this can be house ruled easily enough by saying "All weapon enchantments can go on Ki Focuses". However, Mike Mearls said in his post that that was a workaround, not the real rule. And that sometime in the future, there WOULD be rules on WHICH enchantments go on Ki Focuses. That would make your character illegal as soon as those rules come out.
And in my case, I complain about it because I play in the RPGA where the rule is that if it isn't in the books it isn't allowed. Which means, you can't use any type of workaround for months. You CAN'T use Ki Focuses.