Flagship Android devices need something to set them apart from iPhones whether it is a benefit or not to the end user. Having more and bigger is one way to do that… It started with larger screens, more CPU cores, more RAM, higher megapixel cameras, OLED screens, etc. And for the most part it works when it tricks people into thinking that’s what they need. No one cares about how much memory an iPhone has, except people who think it is an important metric because, “It’s more!”
It takes a constant flow of power for volatile memory to perssist. So even when your device is “off”, the more memory it is using, the more power it will drain. Yes, it is not a lot of power, but it is an area where “efficiency” can make a small dent.