Why do you feel the need to delete your chats? Is it to save space? Would you still do it if you had unlimited storage?
I feel like you think there's something wrong with not collecting and keeping this data. I genuinely don't know why you would.
Changing the default is not a big deal, for sure, but would you still do it if it required 10 minutes of your time every 6 months? If yes, I just cannot believe that you have no reason to do it. Perhaps it makes you feel freer, perhaps you think your device is more organized or cleaner, or something else.
But of course in real life data uses storage, but I feel like most people are on the other extreme and keep too much (data or possessions) because they cannot let go, but chat data footprint is usually minimal unless you receive lots of photos/videos.
You keep saying storage isnt an issue, but having a large digital footprint is just more baggage to manage in future. I want to let these conversations/relationships evolve and change over time, I dont want to keep revisiting them at a certain point.
Each time I get a new phone, I go through and curate the photos/ files worth saving, back them up offline, then start fresh.
Just because you can store everything, infinitely, forever, doesnt mean you need to.