Well, for someone whose business was giving lectures it's natural to see the written word as a threat and to point out its only flaw (there's nothing more than what's written) instead of its virtues. Business wouldn't be booming as much if everyone could access knowledge at any time, anywhere.
Socrates was not “in business” as a teacher and did not charge fees for his conversations. Τhe Sophists typically taught rhetoric and other subjects for payment, whereas Socrates explicitly distanced himself from this. “Writing, Phaedrus, has this strange quality, and is very like painting … if one asks them a question, they preserve a solemn silence.”