If a team is performing badly then they would loose the Test status as Zimbabwe lost their Test status in the past and there is not much countries playing this popular sport as there are only 12 playing countries and in that West Indies select players from around 15 countries and in that Zimbabwe, Ireland and Afghanistan are weak teams as they cannot challenge top teams even at home and if you play the rest of the top countries more often it will be boring. England, Australia, South Africa, New Zealand and India are strong when their are playing at home and if any touring team defeats them then it will be a hard fought game.
I would consider this as a very weak defense of the ICC's decision to include 9 teams in the first division of test cricket.
Zimbabwe lost their test status because of the corruption issues within the cricket board, and not due to the weak performance of the Zimbabwean test team. You can argue that Zimbabwe, Ireland and Afghanistan are weak teams but I am going to disagree. At least Afghanistan deserves a chance to progress to the top division. They have proved that they can compete against the big-3 nations on a regular basis. I would argue that Afghanistan is as good as any of the lower ranking first division teams, such as West Indies and Sri Lanka.