This is something so obvious that it doesn't need a citation, but I think it's misunderstood.
It doesn't mean that the quality of the product decreases, but that the average quality of whatever is made with the product decreases from a user's perspective.
Just take a look at WordPress; I'm going to assume that over time the product itself has gotten more secure and usable due to more eyes being on it and it's adoption rate increasing, but being secure in itself doesn't mean that it can't be used insecurely.
It doesn't mean that the quality of the product decreases, but that the average quality of whatever is made with the product decreases from a user's perspective.
Just take a look at WordPress; I'm going to assume that over time the product itself has gotten more secure and usable due to more eyes being on it and it's adoption rate increasing, but being secure in itself doesn't mean that it can't be used insecurely.