I get why he wont add a practice squad but I can give you an example where the practice squad players are just free agents so why do it.
Say I have a 12th year kicker who will soon retire. I draft a kicker in the late rounds and he booms slightly in camp. He is good but not quite as good as my veteran. When I have to trim my roster from 60 to 53 for the regular season, I have to cut that rookie kicker meaning he will become livid with my team and refuse to sign with them in the future.
If there is a practice squad, I can try to stash him on it in hopes nobody signs him and he can then be called up the following year if my veteran retires.
The same scenario can be made for other drafted players that may not be quite good enough to make the team but would be a nice thing to have come week 13 when injuries mount up and I have to field a team. Basically any rookies that dont make your 53 man roster become free agents for 31 other teams and the drafting team gets screwed.
I can think of dozens of times, I drafted someone that I wish I could of held onto but had to cut. That's the whole purpose of a practice squad