Do you know any country in which people were born, lived all their life...
More on this.
Latvian SSR ceased to exist like the rest of Soviet Union.
Latvia after 1990 was NOT a new country like Belarus or Ukraine.
We restored pre-WW2 Latvia with the same constitution, laws, etc...
And this country IS internationally recognized, even by Russia (who does not admit that they occupied us illegally).
That's why only pre-war citizenships were restored (there was no such thing as Latvian SSR citizenship anyway).
And even some latvians did not receive citizenship automatically if they or their predecessors were not citizens before 1940 - fair game for everyone.

So try to look from this perspective.
Latvia was NOT a sovereign country between 1940 - 1990 - and we had no control about anything that happened here.
If your apartment was invaded by someone and he reorganized it by his taste.
Are you OBLIGED to unconditionally accept EVERYTHING that he had done there after you throw him out?
We are not OBLIGED to unconditionally accept Soviet laws about which we had no control about.

Of course if someone decided to remove citizenship from Russian speaking Latvian citizens NOW,
I will be first to go and protest about it, because every citizen should be equal regarless of nationality.