Not me. She's been married before and if they're not in a hurry to have kids or have them ever then I don't see a "need" for the paper earlier rather than later.
Plenty of other high profile celeb couples have been together longer and either haven't gotten married or got married recently {no naming names}
I don't think anything is wrong with couple who doesn't want to get married but if you are engaged that means you intend to get married. After 3 years it seems strange that you haven't followed through with the intent yet. What is the point of getting engaged if you don't feel the need for the papers? unless it's more of a symbolic thing to them I guess...