It would appear that Kyle Love has surpassed Colin Cole as the back-up DT behind Star Lotulelei and was therefore considered expendable.
The move seems to indicate the Panthers are keen on improving the lagging pass rush.
Panthers have released veteran DT Colin Cole and signed undrafted rookie DE Ryan Delaire from Washington's practice squad
— Jonathan Jones (@jjones9) September 30, 2015
If the Panthers wanted to add a DE I'm not sure why they didn't just call up Rahim Cox as he played fairly well during the preseason.