I still remember a mate laughing at me when we were in the gym and i gave up on a treadmill after 25 minutes. At the time i was into running long events in the Lake District at 10+ hours, yet just couldn't face indoor running for even 30 minutes.
I think it's a very mental thing that some people just struggle with.
Must say i cope better with my Kickr Bike as there's no display, so i tend to just set a power output on my phone and turn the display off and watch an episode and it goes by much quicker without a timer counting in front of me