[Al Skierkiewicz]

I can answer this one.
Way back when, you could do just about anything on mechanical but you were highly restricted on electrical. Those of us electrical types petitioned FIRST, through the feedback process, to give a little more leeway in electrical design by allowing more vendors. The current list is a progression of that request and further year's changes. By limiting the number of vendors, all teams are somewhat restricted to using the same components that are readily available to everyone. Inspectors are more able to make rational decisions when they see components that are available from a small list of vendors. Any questions as to availability can be easily answered on line or by phone. Everyone benefits! Add to this list, parts that are available through regular suppliers, i.e. McMaster-Carr and you have a lot of electrical stuff at your fingertips.