The strategy behind an omnibus bill is to force members of Congress to vote for things they might not want to vote for individually by putting those things in a bill that the members will not want to defeat.
In many cases in Congress, one side wants something to become law even though the other side would not like that particular provision. One thing that can be done in such a case is to put the objectionable provision into an omnibus bill. If the omnibus bill has things that the other side will not vote against (say, for example, funding for a war), the other side can be forced to vote for the thing that they do not like.
Thus, the point of an omnibus bill is to get a provision passed when it would likely be voted down if it were up for a vote on its own.