Why hasn't the fifth and final season of the classic Sailor Moon anime been officially dubbed or subbed in English yet?
There are at least two possible reasons:
1. Financial and legal licensing issues with the companies involved. According to Moonkitty.net, Sailor Moon Season/Series 5 (Stars) is apparently considered as a "spinoff series/season" to the original anime. Therefore any company paying for the rights to dub Sailor Moon would have to pay for TWO separate series under the same brand...a more expensive proposition than if Stars and Sailor Moon seasons 1-4 were to be considered as one whole series package. I have no idea if Moonkitty.net's explanation about the money issue is true or not. Wikipedia does say that the reason that Stars was never dubbed in English was because "Toei wasn't putting it up for licensing." When Toei was licensing Stars to other countries, no North American company has been able to get permission to dub it. This may possibly be because of what Moonkitty.net is saying about Stars being a "spinoff season."
However, for a time since Supers was dubbed and aired in it's entirety in English by Cloverway (Toei's North American subsidiary company) and since PGSM was aired in Japan...ALL possible international licensing rights to redubbing the franchise were impossible to obtain. This is because the rights to license the franchise to the international market were put on lockdown by Toei, Kodansha and Naoko Takeuchi until 2010. Also, possibly even before the lockdown, North American and English language broadcasting rights to the franchise expired in 2004, according to Wikipedia.
The expiration and nonrenewal of the broadcasting licenses in the English language countries in 2004 may be the primary legal reason why Stars was never dubbed into English past the year 2004.
2. Another reason was possibly the possibly controversial content of Sailor Moon Stars and the nature of censorship in English countries. However, most countries other than English speaking ones DID get Sailor Moon Stars...so this secondary reason is not really all that plausible.
In conclusion, the primary plausible reason why Stars wasn't dubbed in English was possibly simply because it wasn't legally or financially available to English speaking countries because their legal broadcasting and licensing rights have all expired without being renewed before they could buy the rights to Stars. The lockdown on the international licensing rights only made the possibility of the Sailor Moon Stars anime season getting an official English release even more unlikely.
The official release of the Sailor Moon franchise licensing from the lockdown in 2011 for the international Sailor Moon revival has potentially made the licensing of Stars possible to English speaking countries...but that's ONLY if the Japanese copyright holders (Toei, Takeuchi, Kodansha) choose to put Stars up for licensing to those countries.