Obviously everybody would love infinite disk space, infinite RAM, infinite I/O, etc. But there are always trade-offs of cost, time, manufacturing capacity, and so on. And since there will always be improvements down the road, you have to cut it off somewhere.
Since these are entry-level products with a first-generation (for Mac) SoC, they decided to get something basic out as quickly as possible as a proof-of-concept that could be used to port Intel applications over and get some real-world testing and use. So rather than dedicating time to designing a desktop SoC from scratch, they repurposed a mobile design which, for obvious reasons, never supported multiple external displays.
For most casual end-users, they'll connect to one external display at most. Many will not use even one. So this provides a good test-bed for maturing the requirements, design, and engineering for future beefier products. I know it's frustrating. But if these initial offerings don't meet your needs, just hold on for a bit. It won't be very long at all before fully mature products are available.
