Connecting GPU chips in order to create more powerful graphic card
Graphics Processors do have special architecture to allow massive parallelizm of operations. The units must be fed with stream of data, yet the results of 3D processing must blend/merge into final image. To make more than one GPU on a PCB, the chips must be specifically designed to provide this expandability in terms interconnect and data sharing. Whether this re-partitioning is economically and technologically feasible and/or effective from performance standpoint is the question. The entire topic was extensively researched by finest Computer Architects for years, see, for example, this AMD publication. The resulting manufacturing strategy is constantly evolving with progress of technology. Just throwing an "idea" to have "more" is not mature.