No, it wasn't.
I'll give you a very real life example.
In 2015 my girlfriend needed to go on a long road trip. But her iPhone was dead toast.
Soooo we go to the Verizon store. The cheapest options were either to buy a 200$ 'flip' phone (not smartphone, just a flip phone) up front, or to get a new contract and lock in.
Mind you, By this time in 2015 it was very easy to find sub-75$ prepaid Android phones. In Brick and mortar stores. Hell Verizon even sold a couple, but you weren't allowed to bring them onto a postpaid plan (lol).
I wound up spending less than 100$ on a Lumia 521 (yeah, lol winphone, but the map app (HERE drive) had great offline map downloading support which suited her purpose,) and putting her on my TMO for a while.
If you looked at the top end of the market back then, yeah, there wasn't much real difference between what TMO did and a normal contract. But at the lower end of the market it made a huge difference, that's why TMO won so much of that market.