In a traditional theft of services, the service is only performed because of the promise of a thief. I.e., a taxi will not drive across town unless I promise to pay them - thus, the driver is deprived of that time/effort. In contrast, both movie pirates and people who choose not to view the movie made no promise to a movie studio.
Sneaking into a concert without a ticket is trespassing.
People who choose not to view the movie are irrelevant to the discussion. Don't try and attach pirates to that group. One group is moral, the other not so much.
Taxis say "I will drive you across town if you promise to pay".
Movie studios say "I will show you this performance if you promise to pay".
The promise is implicit in the act of watching/riding. You don't get in a taxi and explicitly say "I will pay you to drive me around". No, you get in a taxi and say "Take me over there". The promise of payment is implicit.
Sneaking into a concert without a ticket is trespassing.