How do Minecraft Alt Shops get their accounts?

I came across a large number of Minecraft accounts shops a while ago. I know myself that you can crack accounts for Minecraft, Netflix, etc. But I can't really imagine that the account shops can access the data in this way. So I would be interested in how they get your accounts.

Many were hacked, phished or simply taken over by data leaks

Exactly, then automatically check all data leaks with a script / program, whether email and password also fit for Mojang / Minecraft, then email and password are automatically changed and you can sell the account