Decades have passed, people have already crossed the river, and leaders at all levels are still pretending to touch stones by the river! ..... I don't understand the beauty of this joke. .

It means that in the era of reform and opening up, the leader said that he would cross the river by feeling the stones, which means to keep practicing and accumulate experience. Today, people have already gained experience through practice, and leaders pretend to be still in the practical stage and are unwilling to reform because they touch their own interests. The general meaning is that reform can't keep up with practice and satirize leadership!