It is mainly that just because your bitch (and I mean this generally, not yours in particular) is good on paper, isn't enough.
Both parents should be 'proven' ie have done very well in the ring, as well as having perfect temperaments and perfect scores on anything medical (if that is applicable for the breed).
And yes you are right about the reason, no-one should be breeding unless they want something from the litter for themselves, ie a puppy to continue their lines.
Most puppies from a good breeder will come with a (something I can't remember the name of) that will forbid you to breed from them. I think if you were to contact a good breeder and say oooh I fancy having a litter, they would be horrified.
It is not just a case of doing a bit of research and putting a nice dog to a nice bitch, you must be improving the bloodine of the breed.
This is something that really, gets my goat, those who think their bitch is lovely and so decide to breed from her, sometimes it is to have another dog who is similar, but the best way yo do that is to go back to the original breeder for another pup.
I sometimes think byb sounds too strong as somehow it implies cruelty when some people are really just deeply misguided, maybe 'hobby breeder' is better, but to be honest still just as much of a mistake imo.
None of this is aimed at you Slubber, it is just a subjuct that makes me see red and get a bit ranty, hence why my reply may be a bit disjointed, sorry.