Now, if the democrats had more big donors than republicans, maybe they wouldn't? But that's a counterfactual that we can't know. But we do know that Bush 1 vetoed a soft money limit passed mostly by democrats, and that Clinton pushed for one, but didn't get it done.
McCain-Feingold passed the Senate with 48 out of 50 D votes (96%), and 11 of 38 R votes (29%) (and one I (100%)), the House with 198 of 210 D (94%), and house, 41 out of 217 R (19%), 1 out of 2 I (50%). Then it was a mostly R appointed Supreme Court that gutted it. Then a _more_ R appointed court that has continued to whittle it down.
For all that the Democrats don't go far enough, there is a _huge_ difference between the parties on this.