I will confess to personally believing that if you're not going to actually start planning to get married, it seems a bit silly to get engaged. I start to think that they engagement isn't really all that heartfelt.
In a philosophical sense, I'm not a fan of "being engaged" as being anything more than a temporary, transitional state. I don't really like engagement parties, because I don't think this is a stage that should get its own celebration. It's sort of like the time period between being offered a job, and starting it. The "starting it" is the real thing to celebrate; the other stuff is just as administrative preliminary.
So when a couple seems to treat their engagement as its own stage, and not as an administrative preliminary, I tend to wonder why they bothered to get engaged.
Sort of what Oh Joy said, actually.
But, that's mostly an academic or philosophical reaction. How each person/couple lives their own life and navigates this is going to be influenced by lots of things--I don't think there's any neutral *rule* or anything.
And I sure as heck don't say anything, even if I do wonder how you have truly have a fiancÚ for multiple years. A "fiancÚ" is " someone you are committed to marrying"--and I wonder how committed you can be when you've let so much time go by without actually doing something about it. The whole idea is to GET married, not to promise to marry. So if you couldn't bestir yourself to GET the thing you want, maybe you don't really want it.
Also, strictly philosophically speaking, I lament the changes in our wedding industry that make people say, "We can't afford to get married right now," when what they mean is, "We can't afford a big party." What's that bumper sticker? "Don't postpone joy."
I miss the Victorian concept of "an understanding," reserving "engagement" for "we are planning."
But I will ALSO say that I wish people wouldn't run around asking, "When are you getting married" as soon as they hear that people are engaged. We do have long engagements nowadays. And potential guest, it's not all about you. (Of course, sometimes people don't want you to think they're ignoring your happy future, etc., so that's the only conversation starter they think of.)