Because Steamworks is programmed into the game. Some people like achievements too, so we should take them out because some people are irrationally resistant to change?
Steamworks was designed to be modular, it was one of Valve's main selling features for it. Any game released with Steamworks can also be very easily released without it (if not, Direct2Drive and Impulse would be in a lot of trouble)
And your latter half is just nonsense: It has nothing to do with being irrationally resistant to change: Some people don't like the fact that, no matter how remote, Valve controls your ability to play the game in a very easily enforceable way. Its my game, and I'll play it when I damn well please. Same with the movies I buy on DVD: I bought them, so I'll watch them when I want to. If I didn't want to be able to play it on my time, I'd rent it, not buy it.
Once the following is introduced into Steam, I'll have no complaints with it:
-"lending" a game to a friend -- Amazon was able to do it with Kindle books. You can lend a book you bought for your kindle to a friend for 2 weeks at a time -- just like you can lend a real book to a friend.
-Have a system in place to disable online activation,
and have it's implementation be part of the license agreement -- Currently there is only a singular blurb by the PR COO saying basically "Well, I see no reason why we wouldn't do that should we have to" -- Not even nearly good enough. Even worse, the license states the exact opposite: that they have no obligation to do so (and such EULAs have withstood the test of the justice system as being 100% legal). Companies suddenly going under, or being hostilely taken over does not fit into your schedules of "to-dos". Without it being guaranteed, there is no way for their word to be enforced and would be all too easily to snake out of.
While not mandatory, it'd be a wonderful thing if Valve introduced a second-hand market for selling your licenses if you no longer want a game. -- You put a game up for sale and it is instantly removed from your library. Your account is also flagged as having both bought and sold the game, and as such you cannot buy the game second-hand (to keep from the system being abused)