i'm confused though. how come a defendant can challenge the original court's jurisdiction in the enforcement action through a collateral attack?
I haven't researched this specific area of law, but my guess
would be this:
Jurisdiction is a constitutional issue. Venue is not. Although SMJ and PJ are principles derived from the Constitution, venue is purely statutory and was created for efficiency and convenience purposes. Parties can collaterally attack a suit which was unconstitutional, but not challenge a suit which was merely inconvenient.
Subject matter jurisdiction relates to the power of courts to hear cases and controversies under the constitution. It's a federalism issue.
Personal jurisdiction and service relate to the due process which must be given to parties haled into federal court.
Venue is primarily concerned with the convenience of the parties and witnesses and invokes no constitutional issues. 14D Wright & Miller, Federal Practice & Procedure § 3801 (“Unlike laying venue in a proper locale, the exercise of personal jurisdiction implicates constitutional, not merely statutory, concerns”). There is a presumption against jurisdiction in federal courts, but there is no such presumption regarding venue. 695 F.2d at 724