I²C needs 2 lines and that’s it, while SPI formally defines at least 4 signals and more, if you add
slaves. Some unofficial SPI variants only need 3 wires, that is a SCLK, SS and a bi-directional
MISO/MOSI line. Still, this implementation would require one SS line per slave. SPI requires
additional work, logic and/or pins if a multi-master architecture has to be built on SPI. The only
problem I²C when building a system is a limited device address space on 7 bits, overcome with
the 10-bits extension.