"SDA" and "SCL" only have a well defined consistent meaning on the outside of the processor. Inside the processor is a different story. A vendor is free to implement I2C however they wish. They are also free to have different implementations for different processor families.
The ATmega family has a dedicated subsystem that performs I2C communications completely in hardware. The ATtiny family does not. Instead, it has a "Universal Serial Interface" that provides help with SPI or I2C communications. It's like comparing a turbine jet engine to a reciprocating internal combustion engine. They are both capable of moving a vehicle from point A to point B but they do it in radically different ways.
So, why does these libs do not work with the ATtiny4313 ?
The Wire Library is written specifically to work with the ATmega I2C subsystem; something that simply does not exist on ATtiny processors.
The docs show that the ATtiny85 and the ATtiny4313 do have a SDA and a SLC and TWI (I2C) is supported.
I2C is supported but the way that support is realized is different than the ATmega family.