Probably because the Apple Watch is effectively a modern 10 year old smart phone made tiny with an ARM Cortex A series CPU running at nearly 2GHz while the Garmin is a ARM Cortex M series microcontroller doing ~200MHz.

And still the Garmin offers much of the same functionality. It seems Apple is wasting 30 × battery life just to be 2 × "nicer" than a Garmin.

That is the (modern) Apple way. They optimise for smooth experience first¹, other factors second.

----

[1] Actually second, their priorities are money->UX->others - hence being uncooperative with any efforts to improve standard web apps despite the potential user benefits as they could compete with their appstore

My Garmin doesn’t get 30 days but does routinely get 2 weeks, which is fine with me. The battery life is probably the only reason I have never tried the Apple Watch, and I check every generation to see if there has been an improvement. Even the large sport / epic one only gets pathetic 36 hours. It’s mind boggling how Garmin can be so good at this and Apple cannot.

Probably use-case. I only really engage with my watch to check the time and my pulse which I can do with a glance, otherwise the screen is permanently off. The other times are when I'm doing some activity (running, swimming) and GPS is on but for example with running the screen still only shows when I glance at it. Apple still has an enormous amount of room to optimise their hardware and software in this space but I've no idea why they haven't done it yet.

The Apple Watch feels like it's designed as a very small iPhone. It has a lot of unnecessary functionality on-device, like email, a separate iMessage client, and its own Focus settings, which can sync to the iPhone, possibly as a requirement to make the watch operate independently. All these things take up battery power.

Also, Apple sees no benefit having their watches last longer, so they're adding features instead of optimizing them, as long as it hits 18 hours or so.

Yea I see the Apple Watch an extension of iPhone. It's an accessory that integrates with the ecosystem and offers conveniences. I see it as a different product with different use cases that other competing watches.

For most people, the batter is enough for the day of an average use and they charge it at night with their phones.

I don't know about the Apple Watch Ultra 2 however and how it compares.

When you feel the 500+ eyes that read this and go "wow".

Just guessing, maybe Apple doesn't want that, so to not compete in a niche of demanding users with excessively utilitarian needs?