My guess would be because most of the question words are usually written in kana so it was probably just thought だれ would become the most common form. For some reason, the kanji has stuck (probably because it's cool).

It's a very common Kanji and it's being included in the revised Jouyou list.

It's also kind of a nobrainer because it's so damn common how could you forget it at all? It's only 2 radicals Glad to see it's being included in the new jouyou though.

The notion of the jouyou kanji is interesting because the last 500 are common but they're common amount the rarer characters. Then there's 1000 about jouyou which could actually call rare and mean it. Then there's 3000 after that which are almost a joke to call "rare". Then there's the 3000 after that which if not even kanken tests you're probably really never going to encounter them!

zohar wrote:

And then there's 「熊」（くま）which for some inexplainable reason was only recently re-introduced to the joyo list even though it's part of the name of a freaking prefecture for goodness' sake...

I guess there just weren't enough newspaper stories about bears back in the day...

There are currently 13 prefectures (well, 都道府県) that cannot be written with Jouyou Kanji:
茨城県, 栃木県, 埼玉県, 神奈川県, 山梨県, 岐阜県, 静岡県, 大阪府, 奈良県, 岡山県, 愛媛県, 福岡県, 熊本県, 鹿児島県)

All of the kanji from there are in the proposed additional kanji.

They were never "dropped", they weren't on the Touyou or Jouyou list.

Yes, 誰 was one of the first kanji they taught me at school in first year Japanese. I was so surprised to find it wasn't in the Toyo list.

Names are a different situation. As well as the ~2000 Joyo, there is a supplementary list of kanji that can be used in names (it too has slowly grown over time). So quite likely the prefecture name kanji are included in this extended list and so are quite "standard", even though they're not in Joyo proper.

Another point... I don't think how common they are is the only reason for inclusion. For example, 昭和 is probably the only use of 昭 and it's use will decrease over time. However, for political reasons it had to be included in Toyo. Likewise many kanji for archaic units such as 匁 and 勺.

I wonder why they want to increase the number of kanji in common use? Seems like a backward step to me. They should be gradually reducing them over time.