What happen to district 13 why does the capitol show the district on tv?

District 13 was thought to be destroyed by the Capitol during the Dark Days, but it actually survived and became a center of rebellion against the Capitol. The Capitol showcases District 13 on TV to maintain control and instill fear in the other districts, portraying it as a desolate and threatening place. This serves to discourage any thoughts of rebellion among the citizens by highlighting the consequences of defiance against the Capitol.