Actually vidhur was himself not interested to become king though he was wise man and great mentor . He was more interest in religious that is why when Mahabharata start vidhur get irritated and said do what ever all u want I don't care I am going to forest
And it is due to circumstances due to shakuni politics Drishatra become king
Pandu was king initially as vidhur said a king can't see can't run kingdom so that is why inpite of being elder drithrastra was not made king in first place because he was blind instead pandu was made king
But after curse of rishi pandu went to forest with two wives and here hastinapur pur was devoid for king . So shakuni manipulate until pandu come let's make drithrastra proxy king and drithrastra was made proxy king
If pandu was alive then it would be pandu king for long time but since pandu died hence drithrastra become real king of hastinapur