Well, it had to happen sooner or later, but it's likely that hardly anyone expected it to happen so soon: Pokémon GO's userbase has dropped by over 20 percent since its peak usage last month. However, unlike what happened with Nintendo's Miitomo app earlier this year, the reason for this sudden exodus from Niantic's hit app is a bit more complicated.

News of Pokémon GO's sudden development comes via a SurveyMonkey Intelligence report, which estimates that the game peaked at just under 40 million weekly average users (players who played the game at least once a week) in the United States in July. Since then, Pokémon GO's userbase has dropped to just over 30 million, for a 22.7 percent drop.

So, why does the report show weakening numbers for Pokémon GO? According to critics, the answer is obvious: it's a fad.

For what it's worth, they're right, to a certain extent. It's a well-known fact among analysts that mobile games have rather low retention rates, with even the most popular ones retaining only about 30 percent of players a week after they first download the game. On average, mobile games only retain about 15 percent a month after installation. However, Pokémon GO looked like it would be an exception to that rule, with the game having an unprecedented 60 percent retention rate during its peak in mid-July.

If that's the case, then something else might be going on with Pokémon GO. Based on what has transpired in recent weeks, it's become clear that many are simply unhappy with the way Niantic has handled the game.

To be clear, while the game was successful from the very beginning, it was also riddled with issues from the start. For example, when the game launched in the U.S., many people were unable to log in properly since Niantic hadn't prepared for the strain such a large influx of users would cause on its servers. Since then, server issues have been a consistent problem, with the app suffering outages that prevent users from playing the game whenever they'd like.

In addition, there are quite a few things that the game needs to add or fix: for example, a step tracker for when the phone is in standby mode (for eggs), more Pokémon/stuff to do in rural areas and simply adding more Pokemon.

However, the most significant reason for the fall-off from Pokémon GO likely had to do with Niantic's decision to remove the game's flawed tracker and force many third-party apps to shut down. Though Niantic seemingly opened up lines of communication (another issue that fans can attest to) and began testing a new beta system last week, the game developer has done little to explain the nuances of its ban campaign against alleged cheaters and GPS spoofers.

So, is this cause for Niantic to be worried? Not really. Sure, the retention rates are suffering a bit in the U.S., but Pokémon GO is still bringing in over $2 million per day in revenue.

What's more, while retention rates in the U.S. might be falling, the game is still doing well in other parts of the world. For example, the app already has a partnership with McDonald's in Japan, and smartphone games are inherently more popular there.