From 2017-2023 I had Thinkpads and some Acer which was well supported by Linux and sleep was the worse part. On numerous occasions across different devices I'd put the laptop to sleep, put it in my bag, and pull it out in a coffee shop to find it was on and now the battery is down to 50%. Why is sleep so hard?

Ever since Microsoft added "modern standby" it's not a problem anymore. Chips became power-efficient enough that we can just "fake sleep" now, which means disabling all but one core and downclocking it to the lowest possible frequency. My AMD laptop was 400mhz, draining about 15% per day.

Say what you will about Microsoft, but sometimes a strong leader can make good things happen (TPM2 and modern standby)

Well it's being discussed on here in most linux laptops thread.

On x86 it's because linux relies on the acpi tables which vendors don't bother to do properly.

On Apple ARM hardware/linux it's because Apple don't bother releasing any docs.

On other ARM SoCs... not sure. In theory every vendor wants volume orders for phones so they should be able to sleep properly?

It's sad if you're an Apple hardware + software slave and used to just closing the lid on your laptop and having it basically lose no battery for days, especially since ARM.