You don't give free stuff away when you hooked someone on it by subbing, sorry. Also TRIBBLE was free for them, paid by Netflix. So it's easy to throw free subs to please the shareholders at CBS with active, but atm. not paying customers, selling it as a great success.
It's typical that a new pilot has lot of views. Also after a few episodes lot of people stopped the sub, but CBS offered another 1-2 months free subs like two times. That's desperation.