The question you're confused with made sense

It's more about expressing yourself than about getting an official answer from Instagram. I'm curious to know why they don't change that old and childish by modern times icon. And even here someone may know and reply what's the story behind keeping it intact for many years.
Following your logic there's no point in any comments here. Don't like the icon? Wait silently till they'll change it. Found a bug? Report directly to Instagram. Don't like the update? Deal with it. Like the update? Good for you. But people are not robots.