For the most part, these sieges basically replace themselves when they enter the battlefield, either by putting a new card in the players hand or creating an extra permanent in play
Buster Sword During the phase of development we call "Toplining", we go through the design file and determine what the right creative fit for each card will be
There's an argument that an increased modern interest in Cube has made Tolarian Academy the more iconic card over time, despite that one being banned in Commander #9
These offer a lot more for completion than battling online, in fact, and once you tick them all off you can still repeat the battles infinitely for fun
When Self-Assembler enters the battlefield, you may search your library for an Assembly-Worker creature card, reveal it, put it into your hand, then shuffle your library