Coincidence? I think not!
I do not think it is a coincidence that the assembling movement seems to have died out in the late 1980s, just as the personal computer and Internet were emerging. Assembling as a means of distributing creative work was largely made possible by offset printing and photocopy machines which virtualized the page. Whatever you could draw or collage together, you could Xerox or get printed at the local easy print shop. WYSIWYG computers digitalized this virtualization and the Internet remediated the postal system, giving artists living on the margins an even more inexpensive way of sharing their work.
Most scholars situate assembling magazines as part of the "mail art" movement in which artists share work, often printed on postcards or envelopes via mail networks rather than through galleries (see Crane & Stofflet, 1984; Heid, 1991; Janssen, 1996; Lumb, 1997). And while Assembling Magazine does not appear to have survived the transition from offset printing to World Wide Web publishing, its aesthetic and energy inform many online zines, and mail art seems to be thriving with its own archives, electronic museum, and webring, as well as countless online reflections and exhibitions. Post Secrets (#3 on the Technorati top 100 blog list) is a wildly successful Internet take on mail art and assembling. People email the editor, Frank Warren, postcards on which they have created a multimodal "secret." He picks the best submissions and publishes them each week. The results are amazing and moving.