I get why the Apple Watch only lasts for a short time, but why do all these watches that do considerably less have such miserable battery life? Every Mi Band I

I get why the Apple Watch only lasts for a short time, but why do all these watches that do considerably less have such miserable battery life? Every Mi Band I've ever owned lasts for 4+ weeks on a charge. I miss the simplicity of the original Mi Band and with the Mi Band 4 was more open, but they're both fantastic and do most everything I need a smartwatch to do.