By your definition, there were no Israelites until there was a piece of land called Israel.
You are conflating tribal lineage with nationality.
Because they belong to the Moabites tribe. That is not rocket science. 16 And Ruth said, Intreat me not to leave thee, or to return from following after thee: for whither thou goest, I will go; and where thou lodgest, I will lodge: thy people shall be my people, and thy God my God:
Evidently, Ruth had another God.
Then she was admonished to go back to her God. Clearly, they did not have the same God...16 And Ruth said, Intreat me not to leave thee, or to return from following after thee: for whither thou goest, I will go; and where thou lodgest, I will lodge: thy people shall be my people, and thy God my God: