Because people like you are constantly flooding any Macbook-related forum with made-up gripes. The actual owners are generally highly satisfied with the device as-is.
The counterpoint to your complaint, for the 100th time, is that adding a second usb-port at this point in time would not have been possible without altering the design in some way. If it were even something they would have wanted to do, ignoring the fact that the physical design would have to be changed to accommodate it, they still would be up against the limitations of USB-C on this Core-M chipset. The two available USB 3.0 ports are muxed, which would limit bandwidth available to both. That would mean that you could not connect a full speed USB device to each one, you couldn't drive a display from both at the same time, and it would require significant extra wiring to support charging on either port. Further, each additional feature activated on-chip requires more power. That would leave Apple in the position of adding a second port that looked identical to the main port, but was significantly crippled in features and consumed more battery power just by being there. Not very Apple-like. (Take note that the Yoga 3 Pro on the same chipset has just a single usb 3.0 port - the second is usb 2.0 http://www.anandtech.com/show/9061/lenovo-yoga-3-pro-review)
As for the cost of the adapter, this is no dongle. This is a full docking station in miniature. Considering docking stations for other high end laptops typically start at $150 and often approach $300, I find the Apple one to be fairly priced given that it is the ONLY one on the market at any price right now. Sure, I would love more options, but as an early adopter, I can wait, and for now, the Apple one works perfectly fine.
Point on chipset design taken.