Simplify the following text for a Grade 9 native English-speaking person.
Original: According to a paper published in 2005 , Mexico and South Korea were the only other countries comparable to the BRICs , but their economies were excluded initially because they were considered already more developed , as they were already members of the OECD .
Simplified: Mexico and South Korea were the only other countries with economies that are like the BRICs . But O'Neill did n't include these countries because they were considered already more developed , as they were already members of the OECD .