Why do Family Tree keep attaching people that have nothing to do with me and unable to delete?
"Family Tree" does not add anything. Only other users of Family Tree add to the one-world, universal, wiki-tree we are all working in together.
In the detail view of the information and in the change log you will be able to see what users are adding the information you are seeing. Clicking on their names will let you message them.
Usually they will be attaching people because they think you and they share relatives. If they are confused and think you have a relative and they have a relative who are the same person but really are not, then you need to add enough information, sources, and documentation to show these are two different people and families.
While you cannot delete profiles in Family Tree that other people have created, you can delete family relationships that are incorrect.
You can access the Edit Log to see who is making changes. Send them a message about the problem, hopefully you will be able to sort things out. See screenshots.