There are many armor types outside of the DMG/PHB not listed in either one.
There is nothing in the DMG that specifically says armor enhancements can not go on a suit of clothing. Clothing is not defined anywhere in the PHB or DMG. Nor is armor. There is a table listing armor types yes. But that table has had many different items not covered on it that are clearly "armor".
Since the DM has to allow or disallow any magic items, including what is in the DMG, anything magical is therefore a house rule. The DMG just gives a few samples/examples. The only magic items available in a campaign are the ones a DM puts there, making that particular arguement invalid. In fact on the Armor Enhancement table in the back of the DMG, what those enchantments can be placed on is never specifically mentioned or covered at all.
Armor Enhancements on bracers of armor is handled in several sources, as are Armored Clothing, each of those sources as core as what you're counting.
If you do not want armored clothing in your campaign, that's your house rule.