#1. All woman main event at WrestleMania 35
There's really no easy way to say this, but an all female main event at WWE WrestleMania would have been impossible five years ago. Not only is that evident by the lack of interest that fans had in The Women's division at the time, but also by the how little time the storylines were given to flesh out.
With that being said, it's really difficult to name any one factor that made an all women's main event impossible and all variables should probably be looked at equally. Of course one could try to say the company was to blame for not doing enough with the roster they had and not devoting enough time to the development of the division, but the fan interest wasn't there for it either.
In the end, the first ever all women's main event at WWE WrestleMania wouldn't have been possible without Superstars like Becky Lynch, Charlotte Flair, Ronda Rousey, Sasha Banks, Bayley and Alexa Bliss showing just how talented this division is. It also wouldn't have been possible without the fans finally demanding that WWE finally give women a chance.