It's not as if we ever saw a cordial or functional alliance, or evidence of such having existed during one of the off-camera periods. Klingons were always scary, and untrustworthy, and uninterested in pleasing the Feds in any way. Relations may have fluctuated, but attitudes apparently didn't...
TOS already established that arch-enemies may remain out of any contact with the Federation for extended periods of time, becoming no less an enemy in that process. That's inherent in the format: Romulans, Talarians or Cardassians are not heard of until they are
heard of. The Breen are a remarkable exception to that, being name-dropped quite often before finally making an appearance - but then again, they, too, retain an atmosphere of "mystery", now with a twist.