Everybody's been wearing a mask, but there is still the same number of sick people. I wonder why.
この場合、strange も I wonder why もどちらも使って表現できますよ。
I wonder why を使って言う場合:
ーEverybody's been wearing a mask, but there is still the same number of sick people. I wonder why.
「みんなマスクをつけているのに、感染者の数が減らない。なんでだろう」
strange を使って言う場合:
ーIt's strange that we still have the same number of sick people even though everyone has been wearing a mask.
「みんなマスクをつけているのに感染者の数が減らないのは不思議だ」
ご参考まで!