It was clear in the movie that Lockdown transplanted Ratchet's Spark into his forearm. Instead of the spark chamber being smashed and the spark being scattered/lost/dispersed. Lockdown in every instance of the chest shots he fired and the sword he pierced Prime with. Lockdown avoided hitting the spark every time. Perhaps Lockdown did this with most or all of the transformers he captured? The humans were only wanting the Transformium metal chassis and had not interest in the spark. The spark being the only part of the transformer that can not be manufactured or rebuilt. And that either Quintessons and/or Unicron are wanting the wayward transformers hauled home and made to obey? The harvested sparks could either be linked to or installed in new bodies someday to "obey" orders?