Workfront is licensed by user type, with tiers that rise from light contributors and reviewers up to full Plan licenses for planners and administrators. Each tier carries a very different price, and the value of the deal turns almost entirely on the mix.
Adobe sizes the mix toward the higher tiers at signing, because a Plan heavy estate is worth far more than a correctly tiered one. Once assigned, license types are rarely reviewed, so people who only review or contribute keep sitting on expensive Plan seats.
Workfront is also bundled into wider Adobe agreements and sold with implementation and support that blur the per seat cost. Reading the real usage by tier is the only way to know what the platform should cost.