One or more of the following reasons.

• Cost to dispose of it is greater than zero.
• They or someone they know might need it later.
• They plan on doing something with it, but can't afford to right now.
• They don't have a garage or shed to store it in, or they do but those are also full.
• Their backyard has an above ground pool, so no room there.
• They are hoping that someone driving by sees something and makes them an offer.
• They are too overwhelmed working 3 jobs to spend the time and effort to get it cleaned up.

Can't speak for the rural people of the US, but when you're working on a bunch of projects, while the life keeps getting in your way, causing delays, stuff tends to... pile up. For example, I have a car in my living room at this very moment.

Did it seem like a good idea at the time? Sure. 24x7 access regardless of the current weather means more time to work on it.

Did I work on it? Nope.

Was there a wasp nest embedded inside, releasing a steady flow of young wasps inside the house? Absolutely!

The south, and rural areas, in general tend to be poorer. This often comes with a mindset of "don't throw that out, we might need it/be able to use it someday". That's potential future money saved by keeping that crap on the lawn.

Probably for the same reason I have a closet full of computer parts, except I can’t fit tractors and cars in my closet.

Junk removal is expensive and if you're outside of a municipality all trash pickup is done by private arrangement.

hoarders probably, we have a hoarder family members with inside house filled to the brim with junk. its just slightly better than the hoarders on the A and e show.

it might be worth something some day.

Just because they look rusty and old doesn't mean they're junk, but even if they are, there will be no urgency to dispose of them. Most people who aren't minimalists don't dispose of things except for aesthetic reasons, unless they're out of room. Many rural people have a relatively narrow scope for aesthetics that doesn't include what you might call the front yard, and being rural, it's really hard to run out of room. Therefore, there is no urgency to dispose of stuff that has become "junk", and when you do, you will probably do it all at once, as a project, once you start feeling like you're running out of room, which takes quite awhile, so you're very likely to see the development of the junk pile in its intermediate stages.

...southern US...

I'd say that fundamentally it's because it's culturally accepted in those areas.

"Everyone does it" is a frighteningly strong impetus to do something.

In the south it’s also more common to either not have a garage at all or have a carport instead of an enclosed garage. It’s just easier to leave your car or vehicle (tractor) out anyway. Combine that with, I need to sell this or work on it at some point, you park it in your yard and will get around to it someday. Or maybe your cousin might need it one day so you’ll keep it. It’s a bit of an ingrained impoverished idea that you “might need it someday” attitude.

I’m also staying with family that are regularly using tractors pushing 60? 70? Years. I’m not even sure how old they are, but it takes a bunch of parts and pieces to keep these things running. Luckily here though the scraps are either off in a barn or not directly in between the house and the street.

Most of that is "still good. I'm gonna fix it up when i get a chance." If there is still room, there will be more stuff.

1. It’s still in use, but perhaps seasonally or infrequently.
2. It’s gonna get fixed just as soon as I have time.
3. It’s got parts for the other one I have.
4. Might be useful someday. It’s got parts, and the hardware store is 20 miles away.
5. Scrap metal value.
6. The dump is 20 miles away, gonna get a load built up and do a dump run with Jimmy, just as soon as his trailer gets fixed.
7. The dump doesn’t take that thing.
8. Redneck decor.
9. The dump is closed

Based on my limited knowledge, but knowing a few people with yards like that. One is certainly something you are right about.

But also, least to my knowledge in this area, junk yards, scrap yards etc... are a pretty good distance away. So selling/getting rid of large, heavy junk costs more than the scrap is worth. Hence old washing machines etc... In rural areas a lot of people are scraping by on food stamps, barely keeping the power on etc.... would have lost the house years ago if it weren't paid off by the previous generation.

Obviously no HOA's, no one worried about how the houses look, and it's common enough that no one is really embarassed by it.