You recheck the syntax, but everything seems to be just right...
What happened here and why?Not all services support TCP wrapping, to determine if they do we will need to querry them via "ldd" command and see their shared library dependencies, let's take sshd service as an example:
# ldd `which sshd` |grep -i libwrap
libwrap.so.0 => /lib64/libwrap.so.0 (0x00007f04d29fd000)
The presense of libwrap module in ldd output states that the current service supports TCP wrappers.