You don't have to think Blücher alone, but always Wellington and Blücher or Blücher and Wellington. The Allies experience in previous successfull campaigns was not to take on Napoleon unless the odds are very much in their favour.
Any isolated (Blücher) action on their own might lead to disaster. Therefore there was a strong committment to co - operate. This dictated their operational options.
An advance into Northern France, with Napoleon still at large might also create a political backlash and unite France behind Napoleon with la patrie en danger - not without reasons we have the Armée du Nord and not the Grande Armée.