why did they greenlight this with a 200 million dollar budget?

I have heard that it was far lower and then WB decided to spend a ludicrous amount on advertising 





"A big ball of wibbly wobbly, timey wimey stuff" The Tenth Doctor explains all.

Probably needed more for the VFX. Most of the movie is VFX anyway.

Should've spent that money on a better script and actors.

It's the CGI and WB just likes to throw money at everything. Remember when they made a $180 million Tarzan movie six years ago?