Why are the reward redemption levels so different on mypoints?

I have been a member of mypoints for at least 6 years probably even longer then that. I always choose the $50 walmart gift card once I have earned enough points. Look at all these different points you need to get these certain rewards : 6900 - TJMaxx $50 gift card 6900 - Sears $50 gift card 7000 - JCPenny $50 gift card 7000 - Fashion bug $50 gift card 6750 - Old Navy $50 gift card 7500 - Target $50 gift card 6950 - Kohls $50 gift card 7500 - Walmart $50 gift card 8800 - Paypal $50 I love mypoints this is my favorite site but I am just curious why the points vary so much between each reward. My two choices would be between paypal because then I can get the cash and use it for anything I want or wal-mart because I shop there all the time and it would just be using the gift card in place of cash. If I got a gift card towards any of the other places I would have to just get clothes etc which arent always what I need at the time. Since it is over 1000 points more just to get the money via paypal I guess I will stick with getting the Wal-mart gift cards. I only have 3654 points right now so it will be awhile.