What is the purpose of using 成语接龙 to learn 成语?
The purpose is to force one to recite idioms without explaining what they mean.

I believe this kind of recitation is a good way to learn language. Recite it first when we are young; ponder about its meaning later when we have a sound background of related skills, such as logic, critical thinking. This belief is well backed by him, who learned English, German, French, Latin and Greek by recitation, allegedly. Recitation is also an important method to learn in classic Chinese schools.