The devs want everyone to switch over to Microsoft accounts for "improved security and player safety", and they're enticing people to make the change with the promise of free Minecraft capes.

Java Edition will soon require a Microsoft account to play, but you'll at least be getting a free cape for your troubles.

Once that process is complete, your Mojang account will no longer be used to play Minecraft Java, and Mojang is giving everyone who makes the move a free in-game cape.