Updates break things. Often. Almost every time. And you don't notice until you need to use that broken thing. To install new things you may need to update whole system. And you break something completely different.
-PHP7 just released? Yes, we will replace your PHP5 and leave you in agony (compile from source, or wait for AUR and compile it too).
-Networkmanager GUI works with VLANS? Pfff, who uses VLANS, some bug will remove them for you. Use nmcli. Or roll back to older version. Oops, that depends on old library that can not be installed anymore, beacause everything now depends on newer version of that library.
-Wine drag&drop support works flawlessly in one version? Guess what won't work in next? And in next it's the clippoard.
-Prepare for the new world order, Chromium will now train you reading right to left by writing to input boxes backwards randomly.