This problem extends beyond Palantir and internships. Every job interview I have been through, you have to go through a recruiter screen, a hiring manager phone interview, another phone interview with a senior person, first day onsite with 5-6 people, second day onsite with a homework presentation.
ARE YOU KIDDINg ME ?? I have another job, and I have to constantly lie to find time to interview with ONE company. Then these guys all complain about talent shortage and unable to fill up their vacancies. May be, you don't need 20 interviews to determine if a person is a good fit for your role.