#2 Bigger draw at WrestleMania 35
Whether fans want to admit it or not, Brock Lesnar is one of the biggest draws the WWE have at their disposal and having him main-event WrestleMania 35 is a much safer option than going for an unknown like Braun Strowman.
While Strowman is undeniably popular with the WWE Universe, he has zero mainstream appeal, and will not help draw an audience to what is traditionally the company's most popular show of the year.
There is an argument to be made that having Strowman main-event Mania would be an effective way of introducing him to the wider world, but given the fact that the WWE has been taking a beating in ratings in recent months, it seems like too big of a risk at this stage.
Lesnar is a proven hit and he has an excellent history of making memorable moments at WrestleMania.