Why are university presses' contracts so bad?

The (US) Authors' Guild has some thoughts on why scholars should not assign copyright:

"When you assign copyright to publishers, you lose control over your scholarly output. Assignment of copyright ownership may limit your ability to incorporate elements into future articles and books or to use your own work in teaching at the University.” And those are by no means the only potential problems. That’s why we admonish authors never to assign a copyright to a publisher.

And yet:

The copyright grab remains endemic among university presses. To find out why, we recently canvassed several academic authors. Every form agreement that a university press had initially offered these authors contained the copyright grab clause. And yet every author we know of who requested to retain copyright was able to get the publisher to change the agreement.

So?

The problem is that most academic authors—particularly first-time authors feeling the flames of “publish or perish”—don’t even ask. They do not have agents, do not seek legal advice, and often don’t understand that publishing contracts can be modified. So they don’t ask to keep their copyrights—or for any changes at all. Many academic authors tell us they were afraid to request changes to the standard agreements.

One could add a Canadian question:  Why do Canadian academic presses want a waiver of moral rights? (Moral rights: essentially your right to be identified as the author of your work and not to have the integrity of the work tampered with.)

Update:  An object lesson on why not to yield copyright, from this blog just a couple of weeks ago