I have a way I prefer doing things myself, but I'm also very much aware of that there is a typical/standard way of doing things. Be it the "ō" way or the "oo" or whatever, but personally I end up mixing things. Because sometimes "oo" doesn't look as good as "o" (Ookura vs Okura 大倉) not to mention things like 大奥 (oooku, lolwhat, often romanized just as Ooku).
When it comes to things like these, Berryz Kobo etc, I get it. It's that way because that's how it looks more stylish and easier for the English speaker (or other foreign languages, but let's be real, everyone use English as the standard) to pronounce it. Too many vowels are just confusing, no? It is even in hiragana (so thank god for kanji, seriously).