The same reason you get a smartphone or laptop. There's always a better one coming, but you need it.
Really, articles hype up changes that tend to be marginal. I'm not saying that Tesla isn't doing good work or that companies don't improve products. But most of the time, there aren't really big improvements. Cars from a decade ago are fine. Sure, I wish I had CarPlay, but it's fine and there's always something new coming.
At some point in your life, you either learn to live with being slightly outdated or you spend a lot of money.
Frankly, some of it is perception. You've talked about the 2021 Hyundai Tucson and I'm not sure if you mean the 2022 model-year Tucson. The 2021 model didn't have a facelift and the 2022 model is actually all new - more all-new than the Model Y update. It's half-a-foot longer, has an additional 6 cubic feet of passenger space, 8 more cubic feet of cargo space, 3.5 more inches of rear-seat legroom. It has a new engine offering 23 more horsepower (14% more). Hybrid and plug-in-hybrid versions are available. Now, you might not care about any of those changes, but it definitely wasn't a facelift.
What does the new Model Y offer? Potentially 16% increased range, but Tesla might just convert that into cost savings for them. Right now, Tesla is reliant on government subsidies for its profits and with those potentially dwindling over time, they might be looking to cut costs more than offer better range. Will the chassis be better? Maybe, but it's also possible that the first few quarters (or years) could have quality issues. Cutting edge stuff can end up cutting you.
Stuff sounds impressive and sometimes hits the market as "meh". I mean, Mazda's Skyactiv was supposed to be revolutionary. Mazda hasn't been making bad cars, but it's definitely "meh". Fuel economy numbers are worse than most competitors now and power isn't amazing either. A Mazda 3 ends up way behind a Honda Civic for fuel economy and on-par for power. All that cleaner-burning, high-compressions stuff kinda leading to nothing. Mazda says that their Skyactiv-Body is 8% lighter and 30% more rigid, but it doesn't seem to be anything to write home about.
If Tesla introduces a new Model Y with those new batteries, it seems likely that the new models will have a similar range, with some lowered costs for Tesla. Maybe 5% better range and 10% cost savings for Tesla (I'd love to be proven wrong on this). Likewise, the chassis is probably going to be a marginal improvement, but the big thing is likely to be that Tesla has never figured out quality control on their assembly and so they're trying to get rid of that - and pass it off as an amazing feature. And I'm not trying to say that I don't like progress and that marginal progress isn't important. Marginal progress adds up over time. I'm just saying that the new Model Y probably won't be as much of an upgrade as it feels right now. I showed that the Tucson had a lot of new stuff, but to you it's just a facelift. If the new Model Y comes out looking exactly the same with the same range, but there might be some chassis difference you can't see (and realistically probably can't feel), are you going to think that's a major upgrade because Tesla altered its manufacturing in a way that doesn't impact your experience of the product? No, that wouldn't feel like an upgrade at all.
Again, I like that Tesla is pushing things forward and that's important, but car companies are always coming out with "all new" stuff that often doesn't feel like a big upgrade when you actually get your hands on the product. The number of times that I've heard about chassis getting more rigid is just incredible. And, to be fair, cars are much better, but if you get a new car every decade or so and ignore the hype train, you're fine. If you get a new smartphone every 2 or 3 years, you're fine. But they're always looking to talk up how this year's version is revolutionary! Those things rarely happen. If you wanted a Tesla, the Model 3/Y was revolutionary insofar as they had an affordable price point. It seems unlikely that we're going to see a lot more revolutionary stuff. That's not to say Teslas are bad. It's just that "3% more range" or "maybe better cornering if you're going 120MPH...except that's illegal" aren't really revolutionary. If there's another Tesla revolution to happen, it's going to be a $20,000-25,000 mass-market car (that isn't nearly as nice as the Model 3). But look at the Model S. Has there been revolutions there?
To me, this article sounds like the type of thing I read about Apple sourcing displays from new companies. It's more about business sense for Apple than it really is about the product in my hand. The new chassis seems like an attempt to overcome Tesla's quality problems (which also seem to get more complaints on the Model Y). The new battery packs seem like a modest improvement over the old ones (Tesla is claiming 16%) which might show up in improved range, but might end up more in cost savings.
There's always something new. Most of the time it's a marginal improvement. Even big changes can feel like just a facelift if you don't get hyped for them.