Again, the OP is not talking about reasonable questions. Whether one is traveling for business or pleasure is not a reasonable thing for a customs cop to inquire a citizen upon entry into its own country. It is indeed none of their business.
I guess they only want to intimidate you and get you talking for a quick psychological profiling. And the OP responds like I wish everyone with nothing to hide did.
And that doesn't mean entrance lines would take forever. Police adapt their routines to the available time and resources.