USB-3 took a long time to catch on, and the horrible connector for the micro used on phones never caught on. So, while some larger devices such as disks and memory sticks use USB-3 for some years before the C connector came out, the first time phones and tablets saw the 3 signalling standard was when the C connector started appearing.
USB-2 uses a 480 MHz clock. Because of various overheads on the cable, and the relatively crude handshaking mechanism, the highest rate of transferring actual data is about 280 Mbit/sec to a single endpoint, Whereas the first version of USB-3 used a 5 GHz clock. Due to some improvement in the handshaking protocol, this can transfer up to about 4.5 Gbit/sec. Later versions can use 10 GHz clocks, and gang two together to produce something like 19 Gbit/sec.
Power is another case where new power standards were developed that could be applied to the old USB-A connector, but in practice came to market at the same time as the C connector. There is a whole new power management subsystem implemented alongside the main USB signalling system where the two devices can negotiate with each other, and also with smart cables, so that if they all agree, they can raise both the voltage and the current in the cables to deliver much more power.
So it is a number of developments which had been in the pipeline for several years and all arrived at about the same time.
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