First of all that you had some of that wrong which just really bugs me (not judging ) but what i found that was wrong was:
-The chief is not the last Spartan ll because at the end of Halo Glasslands, the UNSC recovered 3+ Spartan ll's and I believe a couple Spartan lll's so maybe e could be because the Spartan ll's are getting old and could've died sometime beofre the events of Halo 4
-When you say cataloging all Forunner technology, i'm assuming you mean all FOUND technology (see what i mean? Little thing like THAT bug me. Still not judging)
Its only two reasons but i felt that I had to say the first one. And Master Chief isn't the only Spartan that had an A.I. Naomi-010 had the A.I. BlackBox.