I have been a consistent player in World of Warcraft since the pre release public beta.
One of Blizzard's main goals in designing games from the beginning is accessibility. This is achieved in many ways.
First, the system and user interface are relatively intuitive. They have been retouched and are easy to understand for people who have never played MMO before. New players can easily access it and learn how to control their characters without consulting external information, which was scarce at that time.
Second, Blizzard pays close attention to which computers its players can access by scanning hardware information and reporting it back to Blizzard's applications. In this way, they can design games that can be played on a variety of systems without the need for high-end equipment to play games. If I remember correctly, I reached level 60 on the 386 processor. The original "vanilla" game even supports playing through dialing.
Third, the world can generally play. In many MMOs today, a group simply leaves town and kills the monster safely. In World of Warcraft, most streaming content from 1 to 60 can be played separately. Some of the tasks are intended to be completed in a group, so they have been clearly marked. Dungeons and subsequent raids also need to be grouped, but in other ways are optional. But for the most part, World of warcraft used to be a fully viable single player game, despite your limited options.
Finally, it has a certain setting. Players who follow Warcraft, Warcraft 2, Warcraft 2: the dark tide, Warcraft 3, Warcraft 3: the frozen throne already have a world and familiar characters. When the wrath of the Lich King appeared, people were eager to get a place in Arthas, and in the later part of the series, they finally had to fight against Deathwing. Most other MMOs have to introduce their world from scratch in order to get people interested. Meanwhile, if you want to have more fun with this game, you will need to buy wow classic gold in game.
Over the years, World of Warcraft may be declining in popularity, but it still has a familiarity side. Many have invested in the game and may not want to participate. When Blizzard released the new expansion, their characters had spent hours behind their backs staring at them, waiting to get ready. Many people may find it difficult to put it into other worlds, which is why many other MMOs that have emerged over the years are hard to survive, let alone thrive.