In Destiny 2, the vendor Xûr appears periodically. After staying for a certain amount of time, he disappears, and players have to wait for his return again. However, some players thought, why not make him stay in the game longer? They decided not to let him go.
Presumably, the pioneer of the method for holding the vendor was Reddit user Hatenotechlab. He stayed with the vendor until the server reset, thereby preserving the instance (a separate player space) where the vendor remained. As it turned out, he began selling particularly good weapons.
Recently, legendary items were added to the vendor's inventory. Legendary weapons roll random perks, so grinding for the “best combination” can demand a significant investment of time and effort from players. However, the vendor appeared, and many were attracted by the opportunity to simply buy weapons with good perks.
On Reddit, one player shared that he spent 15 hours over the course of two days keeping the instance alive with the vendor. According to him, this allowed hundreds of players to gain access to the vendor to purchase decent weapons.
Players are always looking for an easy way to get good items. For example, in Destiny 1, there was the “loot cave”: players took up positions in front of the entrance and shot down spawning enemies.