Well, it didn't help that Dreamwidth was deliberately harassed by a group of trolls with ties to several hate speech organizations, who told lies to Paypal (and, later, to Google Checkout) about what it was hosting. See the dw-news post linked there, and subsequent posts to the community over the next few months, for details. So it is something specific to DW as opposed to LJ, but it's not anything actually about DW, just that LJ hasn't been harassed in that way by that group, and DW has.

And just because I like reminding people of it: from mid-January to the beginning of April 2010, DW was not only unable to receive payments except by check or money order, it was also extending paid account time for free for anyone whose account was expiring and who couldn't pay with check or money order. DW really put its money where its mouth was on its principles.