FYI...Contacted support about removal of iMessage feature and got this reply (below). Followed up to ask "why" and support could not give an explanation.
Beginning October 12, 2020, MyFitnessPal's iMessage app will no longer be accessible to iOS users on versions 20.20.5 and up. Users on versions 20.20.0 and below will still see the iMessage app on their keyboard, but it will no longer be functional.
Your MyFitnessPal friends can still copy items from your diary. Be sure to enable Diary Sharing in the settings menu.
For more information: Retiring iMessage Feature - 10/12/20 (https://support.myfitnesspal.com/hc/en-us/articles/360050370732--Retiring-iMessage-Feature-on-10-12-20-)
Thank you for being a MyFitnessPal member, and stay tuned for some very exciting new features coming soon!