The capital ships were there to retrieve the plans, they knew that the guy who caused the scuffle in the Cantina was on the ship but they needed to be sure he had the plans otherwise they'd be shooting down ships for years on end. They wanted to stop them escaping with something they wanted.

They only sent fighters when Leia got off the Death Star because they wanted the Falcon to escape...something Leia figures out before Han does, they could have launched everything at them but they wanted them to go to Yavin.

Here they don't want the Falcon to escape (it's got cargo on-board that they want) they want them to got straight to The Executor tractor beam.

They have disabled their Hyperdrive but they could still out maneuver the TIEs for long enough to possibly fix it once they figure out what's wrong.

Using capital ships they could block off their options so they have to keep going forward.