Why mediocre CS grads may have a harder time getting a good job in the future

I think its the same for their intentions.

If you are in CS because you want to make a difference in some way, you will have the drive, and be innovative to the field, and will make the difference you want.

If you are in CS because you want a stable paying job, but you put in the work, in the end you will still be innovative and advance teams and become successful.

If you are in CS because you just want the money, and you get low grades not because you tried, but because you didn't, then obviously you are not needed in the cutting edge or high stakes jobs of the field, because you would slow it down.

If you get low grades but you tried, you might find success, because you are looking for success, failing doesn't mean its over, but people who didn't care about the field in the first place are not going to have the courage to come back from failure and rise again.