Because the manual is written for the lowest common denominator. People that don’t dive deeper into how lithium batteries work. There really isn’t any significant harm leaving your car plugged in at 90%, and that setting allows for decent range. Can you imagine if Tesla said "here’s your big battery car, but for best results long term only use 60% of that battery"? The media would have a field day.Well if all that were true (not saying it is not) why not put it in the manual. If their batteries lasted longer then they would make more money. Wondering if you did 50% and pack went bad if you voided warranty by NOT following manual operation instructions? You know the huge amount of data they collect.
So yea, if you want to leave the car plugged in and set to 90% go for it, but anyone who knows anything about lithium ion batteries knows that storing them at about 50% charge is better for longevity. It won’t change the fact that batteries lose capacity as they age over time, but slows down that process a little. If you don’t need the range, keep it in the middle of the pack. When you do need the range, charge it up to whatever you need. That’s part of why, even though I leave the car set to 50% I still plug in. I can always remotely increase the charge percentage should I know I need the extra range.
How often do you completely out of the blue and with no warning, need to drive 240 miles?