[susan53]

Johnson was writing in the 1760s, and the language has changed radically since then. It makes no sense to look at something written 250 years ago and ask "why?" comparing it with what we might say or write now. It's difficult to to find any stretch of more than five words in the sentences you quote, where there wouldn't be radical differences if the writer was using contemporary English. The language of the 18th century had different rules of grammar, used different vocabulary, and had different stylistic tendencies from the language we use now.