Why is "free memory" less than "buff/cache and available memory"?

The total memory of the server is 251Gi, the problem is that in the available column it shows 155Gi while in the free column it shows 1.4Gi. As well as the server makes use of 7.0Gi SWAP 3.1 memory.

[root@lnxsmon3p ~]# free -h
total used free shared buff/cache available
Mem: 251Gi 94Gi 1.4Gi 2.0Mi 155Gi 156Gi
Swap: 7.0Gi 3.1Gi 3.9Gi
[root@lnxsmon3p ~]#