I believe you are right and strange decisions are made and these CGI recreations although they can be convincing.

The Schwarzenegger Terminator 1 CGI recreation is probably the best one I have seen but it works on a level because the character itself did not have to say anything so the face did not need animation.

Tron Legacy and young Jeff Bridges already showing signs of plastic face

It's the facial movements where it still falls over and expression.

Why can't they just find a look a like that can act a like and a sound a like to do an impersonation?

It's not that difficult so many people in this world who can look like other people with the right hair do and make up and so on.

Watching your clip Silverwook and Oliver Reed I thought was quite convincing in Gladiator and then I realised the shot that was CGI with the much whiter beard and the eyes were not right.

Brandon Lees the Crow although convincing the make up of the characters pasty white face and Black lips and eye make up really helped make that much easier to recreate in CGI