Why are bytes treated like the base unit? If bits are the base unit of information, why are bytes treated like the base unit? 

For example, usually values are expressed in Mega/Giga/Tera/Exa bytes instead of bits. I am aware that bits are sometimes used (e.g. sometimes for internet speed), but generally to me it seems like bytes are used as if they are the base unit instead of bits.
For historical reasons.

In the early days and even so today a byte represented the most commonly used data.

A byte represents one character in ASCII.

A byte was and still is the size of the instruction for the most commonly used opcodes at the assembly level. Having the most common instructions in one byte saved the most amount of memory.

It is a power of two so 8 is better than 7,6, and 5.

You can get two BCD digits in one byte.