#3 Creative control and less stringent promos
For many wrestlers, money is not the only thing that matters. Most WWE Superstars have no control over their character and are forced to deliver whatever lines that are given to them. A slight deviation from the script can potentially lead to strict actions.
If you have any doubt, ask "The Monster Among Men" Braun Strowman. In early 2017, while Strowman was still fresh with a mic on his hands, he accidentally used the term "title shot" instead of "title match". That angered the WWE CEO Vince McMahon, and according to Mick Foley, McMahon immediately lost his cool after hearing this.
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Since Strowman was Vince's project, he got away with it. However, other mid-card or undercard wrestlers could get into serious trouble if they were to make such a small mistake.
On the other hand, the creative freedom is more lenient in the independent scene.