Srimate Ramanujaye Namaha!

Lord’s leela is the highest and most difficult to understand.

In general we are suggested to focus on Naama- Guna- Rupa sequentially and then finally on Leela.

In this case , it is possible that Krishna had specific plans that required his presence elsewhere during that time.

But more stronger reason is I have heard that service in separation is the highest form of devotion, where devotion intensifies due to separation. So it could  be the main reason.

And also Lord accomplishes multiple things via one action.

Adiyen.

I have heard that although he had left Vrindavan, he was still present in Vrindavan by his will

I know it’s difficult to understand but I feel this is the best explanation

Jai Srimanarayana