Based on what I've seen, most command-line clients and basic HTTP libraries typically ship with leaner, more static configurations (e.g., no GREASE extensions in the Client Hello, limited protocols in the ALPN extension header, smaller number of Signature Algorithms). Mirroring real browser TLS fingerprints is also more difficult due to the randomization of the Client Hello parameters (e.g., current versions of Chrome)

They use different SSL libraries/configuration. Chrome uses BoringSSL and other libraries may use OpenSSL or some other library. Besides that the SSL library may be configured with different cipher suites and extensions. The solution these impersonators provide is to use the same SSL library and configuration as a real browser.

The protocols are flexible and most browsers bring their own HTTP+TLS clients