DES: histogram differences between plaintext and ciphertext
Lookup avalanche effect either in wiki or our tags here. Essentially, the slightest change (any single bit) of the plain text leads to 50% of all the other bits (on average) changing across the full width of DES' 64 bit block size.  This totally obfuscates any correlation between the plain text characters.

"Caesar" cipher doesn't exhibit avalanche being only a substitution. It simply keeps the correlations and encodes them to other letters.