We’ve been hearing for a while now that Twitter’s go-go-days might be in the rear-view mirror.

But even so, the latest growth forecast for the company still seems pretty shocking for a “new media” participant.

In its most recent forecast of Twitter usage in the United States, eMarketer has lowered its projections of Twitter growth in usage to essentially “treading water” status.

More specifically, digital data research company eMarketer forecasts that by the end of the year, ~52 million U.S. consumers will be accessing their Twitter accounts at least once per month.

That will represent just a 2% increase for the year.

Long-term growth prospects for Twitter don’t look any better. At one point, eMarketer was forecasting growth estimates of nearly 14 million new Twitter users by 2020.  But today, that forecast has been downgraded significantly to only about 3.5 million new users.

In the world of social media platforms, such paltry growth expectations mean that Twitter’s share of domestic social network users will continue to decline. (It’s at around 28% now, which is already a bit of a drop from last year.)

What’s making Twitter seem like such a “passé player” in the go-go world of social media? Oscar Orozco, an analyst at eMarketer, sums up its challenges succinctly:

“Twitter continues to struggle with growing its user base because new users often find the product unwieldy and difficult to navigate, which makes it challenging to find long-term value in being an active user. Also, [Twitter’s] new product initiatives have had little impact in attracting new users.”

Who’s eating into Twitter’s market presence? How about Snapchat and Instagram, for starters.  A host of other messaging apps are also hurting Twitter’s growth prospects.

It hasn’t helped that Twitter has been struggling mightily to monetize its service offering. While it has made valiant efforts to do so, Facebook and LinkedIn have done a more effective job of leveraging their massive user data into attracting advertising dollars.

Facebook is a cash machine … LinkedIn does a respectable job … while Twitter seems almost hopeless by comparison.

After flying high for so long – even to the degree that many companies still speak about social media as one mashup term “Facebook-Twitter-LinkedIn,” Twitter’s decline is all the more surprising.  Poignant, even.