The problem is the LACK of codes available, Voodoo 3. Yes, there are thousands of codes available; 4096 to be exact. But either, more are needed, or someone could reinvent the transponder to use all 10 digits. By missing out 8 and 9, several thousand codes are NOT usable ( 5904 to be exact!). That is why squawks which are close to the emergency codes are in more frequent use.