Why was the Buddy Complex "second season" just a two part finale? It seems like there were expectations for a full second season of Buddy Complex, e.g. from here in March 2014:


  ... the official Twitter account and website for the anime confirmed that the series will still continue.


But then, only three months later, a two-episode finale was announced instead, seemingly to the surprise (a reaction of confusion common in other forums as well, which I share) of many. The finale was released in September 2014. The finale announcement article also concludes with the same note that "the story will still continue" but this seems to be more copy-pasted from the first announcement than an actual announcement (it links back to the same old Twitter post).

Why did Buddy Complex not get a full second season? Was a second season scheduled and then reduced to two episodes because of poor sales or anything like that? Is another season still planned? I don't know Japanese and so searching for sources was difficult. I'm looking primarily for official news and announcements, interviews, etc.
The official tweet you link to simply says: "Regarding Buddy Complex TOKYO MX, that everyone [kindly] watched episode 13, thank you very much! That is to say... To be continued！This work will continue! Please wait for the follow-up. Later on, [we'll] release BD privileged information! #buddycom" (「【バディ・コンプレックス】TOKYO MXにて第13話をご覧頂きました皆様、ありがとうございました！という事で・・・To be continued！本作品はまだ続きます！続報をお待ち下さいませ。この後BD特典情報を公開します！ #buddycom」)

There is no mention or implication within the text that indicates any particular set length of running time, nor even the media type of the promised follow-up. 「作品」 (sakuhin) is a non-specific word for a work of some sort, such as a production, a piece of art, a piece of work, handiwork, even someone's opus.

Thus, the 2014/10/27 post on the official website announcing the 完結編 (kanketsuhen, the last program of a series), which was released November 21st, 2014 and comprised of a two-parter 前編 (zenpen, first part) and 後編 (kouhen, second [after] part), does not in any way conflict with the original Twitter announcement. This means that, no, a second season of TV anime was not scheduled and then cancelled. 「完結編」 (kanketsuhen), by its very meaning, is the last program of a series; to title a release that way is to explicitly state that there are no plans for ever produce a following work such as a second TV anime season.

Therefore, it does not seem that proficient readers of Japanese would have misunderstood the tweet to promise a season's worth of upcoming anime. Someone who reported on the tweet in English for an English-language source seems to have jumped to a conclusion regarding in what sense the 「作品」 (sakuhin) would continue.