Paul's walking

Acts 20:13 recorded Paul's decision to walk instead of joining the mission team.

To understand why he did so might be a futile search and mostly just making own conjectures.

It might be that he stayed behind to console Eutychus the restored youth.
Most probably it's Paul's own quiet time before the Lord to clear his own emotions.

He faced the trials and persecutions from the Jews (Acts 20:3,19,22,25,38)
He faced the departures with the Ephesian elders.
He faced his own uncertain futures
He knew he was bound by the spirit's steps,not his own plans

He gave himself sort of space to pause before the Lord
He created space for his teammates during his absence.
He allowed space for God to touch him

Einstein got a famous formula; E=MC2

Another formula from him too as follows:

Success = Work + Play + Silence

We need rest and silence too to take heed from the Lord.