There are so many tools such as testssl, sslyze to test the TLS configurations on webservers. I wanted to know, why aren't there any tool that checks the TLS client side? What makes it difficult?
It is unclear what you are trying to test exactly. But for browsers there is SSLLabs client test. One can also look at the ClientHello (contains all the supported ciphers, curves, hash algorithms ...).
... wanted to know,
They are not difficult to check, it's just that TLS clients are lower priority to pentesters compared to servers. To check the client, e.g. for supported TLS versions, you would write a utility that starts the server with a TLS version (openssl s_server -accept 443 -tls1_1 -CAfile ca.pem -cert server.pem -key server.key), and examines traffic capture file for presence of "application data" string, which would indicate that the TLS handshake was a success.