As mentioned, T20 cricket is the future. Very few countries were able to spend on test format cricket which is one reason and another thing cricket boards too weren't interested in making the test format cricket survive, giving opportunity for the new teams.
Whether it is the top teams or the bottom ones on the test lineup, players performance were measured through test format cricket that is being played within the countries, like the county and club matches.
Audience interest in Test cricket is decreasing day by day while T20 cricket is gaining a large place in the minds of the audience.Test cricket organized for five days cannot give the same amount of joy that T20 spectators can give in a very short range, but it has become a cause of people's irritation. In test cricket you can't enjoy five days long but to enjoy the fun you have to leave your daily routine and enjoy the fun of cricket. On the other hand, T20 matches of only 40 overs between two teams are over in a few hours and the spectators can enjoy themselves to the fullest. So people's interest in Test cricket is decreasing day by day.
Test playing countries: Australia, India, Pakistan, New Zealand, Sri Lanka, South Africa,West Indies, Bangladesh, Zimbabwe .
These few countries have only qualified to play Test cricket and the rest of the countries have not qualified to play Test cricket. So think for a moment that the popularity of Test cricket will be limited to only nine countries, the rest of the countries are very popular for the T20 format.
80+ countries are playing T20:
https://www.icc-cricket.com/rankings/mens/team-rankings/t20i