We all know that Voldemort had cursed the DADA job (or if he didn't do it explicitely, that he has at least the knowledge about this job beeing cursed because nobody has been able to keep this job for more than a year since 1957).

Then why did he choose to send some of his best allies to occupy this cursed job, knowing that they would probably fail in their mission because of this curse?

Maybe he could have made a try with Professor Quirrel, to see what happens; but even after this first failure, he keeps going on on that downward road: Barty Crouch Jr. (as Mad-Eye Moody), Dolores Umbridge, Severus Snape and finally, Amycus Carrow; all of them bringing on a failure in one or other way.

How many failures does it take before recognising that sending one of your allies to occupy a cursed job is most likely not a good thing?