drop tablespace problem

I have a test schema (NCL) with two tablespaces WIZDATA containing tables of test schema and WIZINDX for indexes
Now these tablespaces are no longer required

SQL> drop tablespace wizdata including contents and datafiles;
drop tablespace wizdata including contents and datafiles
*
ERROR at line 1:
ORA-02449: unique/primary keys in table referenced by foreign keys

SQL> drop tablespace wizdata including contents;
drop tablespace wizdata including contents
*
ERROR at line 1:
ORA-02449: unique/primary keys in table referenced by foreign keys


SQL> drop tablespace wizindx including contents and datafiles;
drop tablespace wizindx including contents and datafiles
*
ERROR at line 1:
ORA-00604: error occurred at recursive SQL level 1
ORA-02429: cannot drop index used for enforcement of unique/primary key

SQL> drop user ncl cascade;

User dropped.

SQL> drop tablespace wizdata including contents and datafiles;

Tablespace dropped.

SQL> drop tablespace wizindx including contents and datafiles;

Tablespace dropped.

Now both of tablespaces have been droped after droping the schema NCL

This is quite confusing for me
Can anybody had encountered this problem?

becuase you had data spanning tablespaces and droppping one of them would have broken your foreign key constraints.

Did you not read the error, the part where it told you EXACTLY what the problem was