As others have pointed out in this thread, the "porch pirate" problem is just kind of not a problem for most people/places. I've never heard of anyone I know having a package stolen off their porch. This is even living in relatively high-density (for the US) apartment complexes. Leaving stuff on the porch is basically good enough, so nobody is in a hurry to "fix" anything about it, except maybe Amazon themselves because even something that happens 0.1% of the time is a big enough problem when you operate at their scale.

I suspect that some of the the same reasons that lockers aren't economically feasible in most of the US is the same reason that the theft isn't a problem: low density. If you're a porch pirate, you need to expect that the value of your stolen goods covers at least your gas and time driving around stealing stuff, plus some risk premium for doing the crime. If the average value of a package is below this amount, the crime doesn't pay. There will still be instances where people haven't done this math, or crimes of opportunity, or just dense stretches where it does make sense depending on the price of gas, but it isn't a nationwide problem.

What problem is that solving for the homeowner?

I get hundreds of packages per year (not an exaggeration) and as far as I know, exactly zero have ever been stolen. Missing packages are invariably delivered to someplace else that must have had a better vibe for the driver that day. (I’ll get pics of proof of delivery with a package that is clearly not at my house.)

In that environment, what problem do I have that could be solved by this, and how much effort (and aesthetics) am I willing to spend to solve it?

Now, if my house shared a wall with two other houses and people walked by my front door all the time, maybe I’d have a theft problem due to greater opportunities for it to happen.

Places with lawns probably don’t have nearly as much package theft just due to less foot traffic.

I'm in the US. Our neighborhood has a multi-slot locker like you describe. It has a small box per house and two larger boxes. The whole thing gets broken in to every couple years, after which the post office will not deliver anything until they fix it weeks later (and they're the only ones allowed to try).

When this happens you have to go to a post office to get your mail.