No single-player GTA game has ever had the success or fame GTA 5 has had by 2021.GTA 5 was first released back on September 17, 2013, to critical acclaim and financial success. Nearly eight years later, the game has sold over 155M copies. It's been through three console generations already, and it doesn't appear to be slowing down any time soon. There is no GTA 6 in sight, so some fans wonder why GTA 5 is this successful.All things considered, GTA 5 has aged remarkably well for a 2013 game. Its gameplay is still solid, and fans (both new and old) continue to buy it. There are also other games and mods that make GTA 5 so popular:GTA OnlineGTA RP serversGTA 5 is still one of the most relevant video games, even eight years after its initial releaseThree iconic protagonists (Image via Rockstar Games)GTA 5 is the type of game that even casuals know about, regardless of whether they like the game or not. The Grand Theft Auto series has that effect as a whole, but GTA 5 stands out as the most recent and longest-lasting single-player game thus far.Its critic scores on Metacritic average from 96 to 97 depending on the platform. Naturally, its user scores are still noticeably lower, but they're still highly positive overall. Even if one hates how much Rockstar Games has milked it, some of its detractors still love how the game plays.It's easy to see why GTA 5 has sold so many copies (Image via Rockstar Games)This game has also won several awards throughout the years, such as:Most Anticipated Game at the 2012 Spike Video Game AwardsGame of the Year at the 31st Golden Joystick AwardsGame of the Year at the Spike VGX 2013Best Soundtrack at the Spike VGX 2013Best Technology at the 14th Annual Game Developers Choice AwardsOutstanding Achievement in Gameplay Engineering at the 17th Annual D.I.C.E. AwardsBest British Game at the 10th British Academy Video Games AwardsBest Game Design at the 10th British Academy Video Games AwardsBest Multiplayer at the 10th British Academy Video Games AwardsBest Remaster at The Game Awards 2014Best Game Expansion at the 2019 Golden Joystick AwardsGTA Online's success is connected to GTA 5's successThe latest update even brought back a familiar protagonist (Image via Rockstar Games)The GTA series used to go through several single-player games in a decade. However, recent years have taken a different approach; GTA Online is Rockstar Games' cash cow, having received several updates throughout the years.By comparison, the single-player GTA 5 campaign has gotten nothing in several years except for the upcoming Expanded and Enhanced Edition. That version of GTA 5 will be available on the PS5 and Xbox Series X|S, which will help contribute to the game's terrific sales.Rockstar Games@RockstarGamesGTAV and GTA Online will now arrive on PlayStation 5 and Xbox Series X|S March 2022.Featuring technical and graphical improvements across the entire experience including performance enhancements for select vehicles in GTA Online, and so much more: rsg.ms/61d9df32:00 AM · Sep 9, 2021148752418GTAV and GTA Online will now arrive on PlayStation 5 and Xbox Series X|S March 2022.Featuring technical and graphical improvements across the entire experience including performance enhancements for select vehicles in GTA Online, and so much more: rsg.ms/61d9df3 https://t.co/gIrXn6fFQXThat said, GTA Online's success is still partially why so many gamers purchased GTA 5 back in the day. Keep in mind that GTA Online didn't have a standalone release until March 2022. Anybody wishing to play GTA Online had to get a copy of GTA 5.That said, its success isn't solely tied to its multiplayer counterpart. The game is more than capable of standing on its own merits.The de facto GTA title for several yearsNo other single-player game in the series has been the main game for this many years (Image via Rockstar Games)Many gamers have grown up with GTA 5 in the same vein that older kids grew up with the previous Grand Theft Auto games. In this case, GTA 5 has been the main title for far longer than any of its predecessors. Nostalgia is a powerful emotion, especially when coupled with a critically acclaimed game.One side effect of being the de facto single-player game in a hugely popular series is that the game's modding scene is incredibly robust. There's an extensive amount of mods that appeal to most players if they care to look for it.One of those mods is connected to the concept of GTA RP, a popular idea that took 2021 by storm amongst the gaming community.The rise of GTA 5 RPNoPixel is the RP server that most English-speaking gamers would recognize (Image via Rockstar Games)GTA RP has technically existed before GTA 5, but its recent rise in popularity is largely attributed to that game. Several immensely popular servers, such as Marbella Vice and NoPixel, have been instrumental in getting people to play a game that uses GTA 5 as its foundation.That's not even mentioning how many RP servers there are. Some fans might even be surprised to hear that GTA 5 was the most-watched game of 2021, largely thanks to the numerous RP servers. For those that don't know, there is no GTA RP category on Twitch, but there is one for GTA 5.GTA 5 RP continues to evolve throughout the months, which only serves to help make GTA 5 even more relevant.