You are confusing patents with copyright. Patents were meant to encourage people to disclose. It was taken for granted that people will invent things regardless of patent protection - they will just keep their inventions trade secrets.
Depends on the industry; there are plenty of places where trade secrets aren't viable (e.g. medicinal chemistry, where it's trivial to reverse engineer a drug).
Maybe so, but nevertheless patents were not "meant to encourage people to invest".