16 MHz core and memory sizing — what fits
The 16 MHz clock is the ceiling for this STM8 core; at that speed the Flash requires zero wait states, so instruction throughput is one cycle per byte for most opcodes. The 2 KB RAM handles a few hundred bytes of stack and a modest frame buffer; the 1 KB EEPROM is useful for calibration constants or fault logs that survive a power cycle.
The wide supply range (2.95 V to 5.5 V) means it can run directly from an unregulated battery or a 5 V rail without a separate LDO, saving a few cents and a component on the BOM.