You're probably right but English, as well as UNIX, has conventions which are widely used. Going against them requires a lot of work and I'm not sure that the benefits are worth it.

"concatenate" is a lot more known than "catenate". And I'm pretty sure that even "concatenate" is quite low in usage compared to a more common verb (or set of verbs) which could be used to describe what cat does ("show", "join", "merge", "unify", etc).

Anyway, I was mostly ranting since at this point both "concatenate" as a de-facto standard term and "cat" as a default UNIX tool will probably outlive me and most likely my descendants as well :)