The Wonder Woman we met in Batman v Superman was meant to be a hero who'd spent decades hiding away from the world, discontent with what Man's world had become - very different to the Wonder Woman we left in her solo movie. The reason for the difference? It didn't feel right for Diana, according to Gal Gadot.
Speaking to the press during Justice League's promotional world tour in China, Gadot discussed the discrepancy between how Wonder Woman ended and the Diana of Batman v Superman - and basically, the decision was made to retcon the background of Diana's abandonment of the world for Wonder Woman because it simply didn't fit with the tone they wanted to strike for the hero:
None of us knew exactly, exactly, the back story of Wonder Woman. And once they decided to shoot the solo movie for Wonder Woman and we started to dig in to understand the core of this character, we realised that, actually, there is no way that Wonder Woman would ever give up on mankind.
The reason why she left the island was because she wanted to make their lives better and safer - they are her calling. So, I'm giving you a very honest answer, but it was - sometimes in a creative process, you establish something that is not necessarily the right decision, but then you can always correct it and change it. So Wonder Woman will always be there, as far as she's concerned, for mankind.
Wonder Woman makes a huge deal out of Diana's compassion. It's the driving force that carries off Themiscyra, across No Man's Land, and into and beyond her fight with Ares. After going so far for so much, the thought of her just casually abandoning everything until Clark and Bruce started beefing with each other is... weird, and not a good fit for the character at all.
It's for the best that it was changed for Diana's solo movie - after all, that hope and love was part of what made it so damn good in the first place.