To contrast, a sword +1 is always useful in every situation. It's an amazing weapon, and the fact that it can also hurt many creatures that would resist normal weapons is simply a testament to how amazing it is.
I feel most people miss this completely.
Magic, like science, has to be learned at some point. You can't just say, "It's magic, stupid. Just roll with it."
Well, you can, but some folks like to do more.

In the world, characters are constantly learning, evolving and that process involves trial and error.
As GMs, we try to apply some logic and consistency to our world, even if those qualities aren't immediately apparent to our players. And I'm only human, so I bring those things that are part of my experience to my game world.
My experience says that unless I've "industrialized" magic, almost everything I do will be a personalized undertaking.
Book standard spells are reliable BECAUSE they've been repeated and only those aspects that work have been recorded. All the "flaws" have been removed from the process. But then there's no room for flexibility.
That's why sorcerers and metamagic are so powerful, IMO. They can improvise spell variants on the fly.
By the same token, people creating items are creating them one at a time. It's not like adding 2+2, or memorizing a spell. In a developing world where item creation is not reliable, you're not necessarily going to find a "perfect" +1 item. I think back to stories I've heard about the old West, where guns and bullets were originally individually manufactured, and mismatched tolerances were one of the reasons they were so unreliable. (I don't know how true that is.)
Such a simple creation, that provides a perfectly reliable effect with zero drawbacks? In my world, that's nearly an artifact unto itself. No software bugs. No ink that runs out. Doesn't talk back or stick in the holster? Doesn't have some heraldry or smith mark that someone could come at you for? Just a +1, every time. Amazing.
Imagine, for a moment, that a wizard has to create an item to "graduate" his apprenticeship. Something minor, or at least contribute to the creation of another item. His thesis, so to speak. Trust me, that item isn't going to be perfect. And even the experienced artificer? How many bad designs did he have to wade through before he succeeded? Did they all get destroyed? I'm figuring a LOT of flawed items are out there before you find a good one.
This isn't necessarily how items were created (or come into being) in my world, but it's one possibility. But I do have a REASON things are they way they are. Most items come with a price to pay or constraint to manage. Pure, perfect items are extraordinarily rare, or mundane to certain locations only.