Why does Socrates feel compelled to defend himself against his old accusers before his new accusers?

The reason is, that in his days there was in Greece no real science and knowledge about nature. Ancient Greeks obeyed the orders of wise people like Solon and believed, that it leads to their harmony with the Universe. This was misused by sophists, who also give payed advices. Socrates violates this rule because he laid the first steps to science by denying the biased truths of people about morality, religion etc. This was unpleasant to them (unlike the payed advices of sophists) and they accused him from doing something forbidden, which they united with unnecessary things and witchcraft. By this way came into existence myths about Socrates and he was compelled to deny them first...