We actually had been discussing this within the team and the main issue is that we are often making changes to sentences here and there and because we will only be rerecording the one audio, the coverage will slowly decrease until only a few of the original sentences remain unchanged.
Even now, the coverage is already down because we adjusted a lot of sentences before doing these new recordings.
From a long time user’s perspective, I can understand why that is probably not the end of the world, but for new users who come across it, they would have no idea why only some sentences seem to have an alternate voice and others don’t.
御願い致します 
自分の声を録音で聞くって変な感覚で、私はそこまで自分の声が好きではなかったのですが、気に入って聞いてくださった方もいたと知って、とっても嬉しい気持ちです 
文法セクションの録音に関しては どうなるか分かりませんが、日記は恐らく消されずに ずっと残ると思うので、そこで聞いていただければ幸いです。約束は出来ませんが、日記の方には、たまに戻ってくることも あるかもしれません 
