The other possibility is not wanting to disrespect whatever belief/superstition the person making it has. It's kinda like finding a roadside shrine to something. It might look like trash, but it's good manners not to fuck with it unless there's a good reason to do so.

The likelihood of nastiness growing in there is a damn good reason by itself, though. I dunno if you've ever read up on any magical practices (as opposed to stage magic) around the world, but some of the stuff that goes into this general kind of spell/working/prayer starts out less than pleasant to interact with.

Urine is a very common pick for various reasons (depending on the belief structure). I've seen "recipes" that include blood, semen, menstruum, or other body fluids. There's various oils that get used, and sometimes (very rarely) mild acids. Water is a fairly common choice, but you're still dealing with an unknown level of possible contamination there.

And that's before any of the ingredients have a chance to steep in there like some kind of dubious tea. I can't think of anything I've ever seen listed for this kind of thing tad would be a contact poison, but I still wouldn't poke my finger in there to find out.

With all of that, and no useful reason to set up and test what's inside, why bother? Curiosity isn't usually a valid case for expenditure of public funds when there's no threat to anyone or anything that can be "fought" against.

As a tangent, you'd be amazed how common this kind of practice is, even among people far aren't otherwise involved in any religions or systems that involves directly using magic as part of the belief. You'll find folks that will believe in small things like this, but reject any other form of "spellwork". Even otherwise devout Christians/Muslims/Jews can pick up individual practices like this as a matter of tradition in their area or family, despite there being prohibition against things under the general heading of magic or spell casting.