Why a cruiser would not tow the merchant away

Could Birmingham have towed Vincent de Paul faster to escape the Japanese cruisers?

Possibly, but towing would restrict the cruiser's ability to screen the merchant ship and would still be limited by towing gear and the merchant hull.

Towing would compromise Birmingham's freedom to manoeuvre between the merchantman and the Japanese cruisers. The British screen already had to divide its attention among three opponents, with Ashigara able to seek a route past Birmingham and Folkestone. Towing speed would also be constrained by the strength of the lines and the characteristics of the merchant hull. Folkestone was better suited to the task than a cruiser, but even that choice would sacrifice part of the escort formation's freedom of action.