Each controller and subcomponent on the motherboard needs a driver that correctly puts it into low power and sleep states to get battery savings.

Most of those components are proprietary and don't use the standard drivers available in Linux kernel.

So someone needs to go and reverse engineer them, upstream the drivers and pray that Apple doesn't change them in next revision (which they did) or the whole process needs to start again.

In other words: get an actually Linux supported laptop for Linux.

Apple does tons of optimizations for every component to improve battery life. Asahi Linux, which is reverse engineered, doesn't have the resources to figure out each of those tricks, especially for undocumented proprietary hardware, so it's a "death by a thousand cuts" as each of the various components is always drawing a couple of milliwatts more than on macOS.

For optimal battery life you need to tweak the whole OS stack for the hardware. You need to make sure all the peripherals are set up right to go into the right idle states without causing user-visible latency on wake-up. (Note that often just one peripheral being out of tune here can mess up the whole system's power performance. Also the correct settings here depend on your software stack). You need to make sure that cpufreq and cpuidle governors work nicely with the particular foibles of your platform's CPUs. Ditto for the task scheduler. Then, ditto for a bunch of random userspace code (audio + rendering pipeline for example). The list goes on and on. This work gets done in Android and ChromeOS.

It absolutely is not awful. You are doing something wrong then. It's not as good as on macOS of course but it's still great. I get 8-10 hours.

Asahi doesn't yet support all the CPU power states etc. This is a known limitation, not sure how easy it is to reverse engineer though.

This is the case with most (all?) laptops running Linux regardless of hardware unfortunately.