I think their strategy for this trailer is to get the audience that normally would not see this movie, the people who are already committed to watching this when it's released are still going to watch it no matter what.
This trailer was for the typical action movie fan who is just looking for a fun action packed film with some comedy sprinkled in, hence the Doomsday reveal, most casual fans are not that familiar with Doomsday or the Batman/Superman dynamic and why they are even fighting since they are both heroes, so they show them some big cgi monster, heroes teaming up, some one liners and campy comedy to get the casuals. DC/Warner absolutely need this film to be a financial success which means they need a trailer that will appeal to a more general audience, I think thats what they are going for and the decision to reveal Doomsday.
Civil War trailer does not need to take risks and show Spiderman since Marvel films are already very successful and they basically sell themselves.
