There is a rather basic reason why there are players on the practice squad and other players on the active roster.
It's not all that complex but just in case it seems mysterious let me lay it out here:
The coaches - - the ones who see these guys in practice every day and the ones that are responsible for putting the team in the best position to win on a week-to-week basis - - think the guys on the practice squad are not as good as the guys on the active roster.
Now, if it is true that there are three or four guys on the practice squad who really are better than the guys on the active roster, then you have to indict the coaching staff and the guys who do "pro player evaluations" for the team for "getting it wrong".