Carr is only under contract for two more years. Were the Saints to make a coaching (and/or GM) change, there are outs before then. Having let Winston walk, unless you're ok with Hill as QB2/TE/FB, they had to make a move at QB.
As for CB, I agree re: the depth vs depth at TE. IMHO, CB, TE and WR are the most often injured in the NFL. I suspect that with CB/WR, once you are a little slower due to injury, you're ineffective.
At TE, I think it's a function of being the El Camino of positions. Is an El Camino a truck or a car? Is a TE a receiver or a lineman? Having to do two different jobs means that if you suffer some kind of injury, if it makes you ineffective as a receiver or a blocker, maybe you can't be on the field as a TE - and so that embiggens* the scope of injuries that can make you a scratch.
*from the Simpsons