The cause of the game's death is COVID-19, as the discouragement of unnecessary travel over the past year and a half has lowered the player count of the game.
The announcement came in January, when Mojang said they
[had] made the difficult decision to [...] end support for Minecraft Earth in June 2021.
The game has been removed from app stores, and all content and service support for the game has now ended, making the game unplayable even if it is still downloaded on your phone.
Minecraft Earth was an augmented-reality game in the vein of Pokémon GO where players had to wander around their world to collect resourced and go on adventures.
It originally was released in beta in July 2019 with a gradual geographical rollout, fully releasing that December. Support ended 30 June 2021.