My retained legal counsel suggests that it's not uncommon for business entities to agree to the broad strokes of a deal (milestones, payments, royalties, tenors, etc), but then the lawyers have to do the job of cleaning up all of the operational details and contingencies that the executives didn't think about (what constitutes performance or lack thereof? what recourse do we have under X/Y/Z situations? etc). Often deals are signed in escrow while the lawyers work out the details, to be executed upon agreement by the legal teams.

In other words, apparently it's completely legitimate for it to take a while, even if "everything" is agreed upon. Blew my mind too.