I was taking a look at the poison rules and some things came to my mind. Injury and ingested poisons are simple enough (although I'm going to houserule that you don't lose an injury poison on a miss). I'm trying to understand, however, the other two types.
Contact poisons: Let's pretend that not being able to apply it to a melee weapon attack makes sense. Can I apply it to a crossbow bolt? Can I just throw the bottle into someone's face? I'm trying to understand exactly how this works.
Inhaled poisons: Those are a lot more understandable, but there's still one thing I'm trying to get. Do I create this cloud of poison by throwing the bottle at a point? If so, what's the range for this?
I can maybe... MAYBE see the balance reason for inhaled being adjacent to you, but how on Earth should I explain that? My Alchemist player was asking the other day how long he could throw a bottle of inhaled poison and I don't think "you can't, this small bottle of liquid weights 200 pounds" is a good explanation, haha.
I'd just treat inhaled poisons as bombs, really. I can't see why you wouldn't be able to chuck them either. Any explanation I can imagine to justify a bomb in a vial also works for a poison gas in a vial.
I can't imagine it being that much of a balance issue, unless the inhaled poisons are significantly stronger than the existing bombs.
I believe the reason poisons might be lost on a 'miss' is that misses reflect striking someone and the blade sliding along their armor/shield/padding/weapon/etc. So I believe the premise for if you miss, if you didn't just completely WIFF the swipe, your blade likely impacted something that may have removed enough of you poison to reduce its to the point of being ineffective. I halfway think I'd seen a past rule that if you hit AC10, but didn't penetrate the AC, your poison was lost.
Granted all of the above, is conceptually pretty simple if you're willing to think it through, but it would be easy enough to understand why they might simplify it to... miss therefore gone.
Other options that wouldn't have to be too difficult would be to give a flat check DC5 or DC10 to still have it poisoned after a missed melee attack. Or you could reflect the potential loss of some poison meaning after each miss, you reduce the DC of the poison by 1. (or some specific amount)
But I think that is the thinking behind poisoned weapons ceasing to be poisoned after a miss.
Loss on a miss would be less awful if it didn't take 3 actions to poison something, or if poisons had enough scaling to be useful at all levels... but oh well. Rogues CAN use poison with a feat, I suppose.
As for contact poison, I've used it several times and my own players did as well, mostly with "friendly face" villains. Exchange something coated in poison, coat the corner of an incriminating document, smear it on the inside of a pouch... But it's not a combat enocunter thing.
Well contact poisons are not going to be very useful in combat anyways, almost all or maybe all of them have a oneset timer of 1 minute, which is longer than most combat encounters in their entirety. I just don't see a need to create an in-world restriction that makes no logical sense to balance something that doesn't need to be balanced.
Apart from the scaling thing I don't think poisons are in a bad place, it's more of a narrative issue for me. Not being able to apply a contact poison to a crossbow bolt or not being able to throw a vial of inhaled poison because "balance" is very immersion breaking, in my opinion.