Q:

Why don't we use simple binary values to compress data

In Huffman algorithm we form a tree and than replace each character with the tree value of 1 and 0, why don't we simply use the binary digits like a=0,b=1,c=10,d=01,e=11 and so on than replace them with the characters and when decompressing apply the reverse and replace the binary digits with the alphabets.
Like this:
character Huffman-code binary-code
a            00            0
b            01            1
c            101           01

and so on...

A:

The important condition for the Huffman codes is that no two are a prefix of each other. If you just renumber them (as I think this is what your suggestion is) you lose this property.
To see why this breaks, look at "01" as the output. In the non-Huffman version it might either be "0" followed by "1" (thus "ab"), or "01" (thus "c"), you can't tell which.

