Why task forces displaced the single fleet battle

Did treaty-driven fleet reductions cause task-force operations to replace the strategy of one massive fleet engagement?

Only partly; the larger cause was geography, because Pacific and global wars required dispersed forces across far greater ocean areas.

An Anglo-German war concentrated major fleets in the confined North Sea, but prospective conflicts involving Britain, the United States, or Japan stretched across enormous ocean areas. Those distances required forces to divide among many operational tasks instead of remaining assembled for one decisive encounter. France and Italy retained the concentrated model longer because the Mediterranean offered a comparatively bounded theater.