The first thing to realize is that even with the current trend towards planned obsolescence, repeated surgery wouldn't be a necessary consequence. This is because all the actual "inserts" have to do is interact with your braincells: at their core they're simply an I/O device, replacing your mouse, keyboard, speakers, monitor and so on. All the stuff we consider "upgradable", such as processor power, memory and so on, can be placed elsewhere. You could replace a section of the skull, or insert it under the skin if thin enough. For that matter, it wouldn't be a stretch to just connect the inserts to a low energy WIFI chip, and have all the upgradable stuff outside the body. As to the "why", it's because mesh inserts would (potentially) be the ultimate IO device. It's a full 3D monitor so massive it covers your entire field of view, with a resolution that hits (or maybe even exceeds) the limits of human vision, and speakers with perfect pitch and absolute positioning. You can type as fast as you can think, manipulate programs/data simply by "willing" the change instead of using a mouse as a proxy, and convert creations straight from your imagination into media files. Okay, those are extreme variants, but the difference between that and the basics is software, not hardware. On the other hand, even without any of the stuff above, inserts would allow more influence over your body, and could provide health information. Blood pressure, insulin levels and dietary deficiencies could be monitored in real time, whilst hormone and neurotransmitter levels could be manipulated to enhance mood and attention, re-enforce brainwave patterns, promote weight-loss/gain, prevent unwanted pregnancy and so on. I may be a tad zealous, but the ability to directly monitor and alter brain activity is one who's potential and importance cannot be overstated.