Why is the dotted i (І / і) and yi (Ї / ї) from Ukrainian not present in Russian?

Question

I noticed the absence of the dotted i (І / і) as well as yi (Ї / ї) within the Cyrillic Russian alphabet. I wonder why these two letters are not shared, when they are vowels and fundamental in Ukrainian.

Answer 1

Some of the letters, including the dotted i, were eliminated from Russian alphabet during Russian Orthographic Reform 1917-1918.