You aren't performing your test properly. Encryption doesn't output random text, it outputs bytes of data (0-255). It should be obvious that compressing text is possible.

$ dd if=/dev/urandom of=test bs=1k count=10

$ cat test | gzip -9 > test.gz

$ cat test | bzip2 -9 > test.bz2

$ ls -al test*

-rw-r--r-- 1 r1ch r1ch 10240 Jun 28 16:30 test

-rw-r--r-- 1 r1ch r1ch 10739 Jun 28 16:31 test.bz2

-rw-r--r-- 1 r1ch r1ch 10263 Jun 28 16:31 test.gz

Random data is not compressible.

$ dd if=/dev/zero of=test bs=1k count=10

$ openssl enc -in test -aes-256-ctr -out test.encrypted

$ cat test.encrypted | gzip -9 > test.encrypted.gz

$ cat test.encrypted | bzip2 -9 > test.encrypted.bz2

$ ls -al test*

-rw-r--r-- 1 r1ch r1ch 10240 Jun 28 16:32 test

-rw-r--r-- 1 r1ch r1ch 10256 Jun 28 16:33 test.encrypted

-rw-r--r-- 1 r1ch r1ch 10737 Jun 28 16:34 test.encrypted.bz2

-rw-r--r-- 1 r1ch r1ch 10279 Jun 28 16:33 test.encrypted.gz

Encrypted zeroes are not compressible.