I don't use IG although they dearly want me to, giving me a popup every time I visit, but let me talk about FB for a second (and btw FB wanted to enable cross-platform messaging on the platforms they own - Meta - which seems anti-trust-y) - when they introduced encryption on FB, they made it mandatory. They opted everyone in, and it broke Messenger. If you delete cookies you might also delete messages. Isn't that convenient?