In another place in his writings, Baxter put it another way: he said that he started catechizing because he realized that his sermons ("...and now, 17thly...") were over most of his people's heads. Apparently, it never occurred to him to simplify and shorten his sermons.
That would be one way of alleviating oneself of the duty to carry on the ministry from house to house as well as in public -- just perform the public ministry like you were in someone's house. But I doubt Mr. Baxter's conscience could have managed to excuse it.