Comcast knew they weren't going to outbid Netflix (or Paramount) for the WB assets, so instead they are striking a deal for the use of those properties in their theme parks. The terms of that deal will be inherited by Netflix, after the acquisition (presumably) goes through.
Universal wants to make a deal now, before Netflix has control over those assets. Universal has probably always wanted to expand their partnership with WB for these characters, but was never in a rush to do so. But now it makes sense for them to lock-in the DC characters (like they have with the Marvel characters) before Netflix takes that option off the table, because they want to build their own theme park. Which isn't THAT far-fetched considering their exploration of the themed entertainment space with projects like Netflix House.
Also WB is going to be focused on revenue in the short term at the expense of long term strategy. So this deal makes sense for them as well.