Why battlecruisers lost their distinct role

Why did battlecruisers become less relevant in the Second World War?

Fast battleships covered their heavy-gun role, while aircraft carriers could project striking power far beyond gun range; the decisive issue was reach rather than a single ship type simply replacing another.

Battlecruisers were squeezed between fast battleships that could perform most heavy-gun tasks and aircraft carriers that responded at far greater range. Fast battleships retained the armour and firepower needed for line-of-battle work while matching much of the older type's mobility. Carrier aircraft could arrive first and keep striking before a gun-armed ship reached effective range. The capital ship's decline was therefore chiefly a problem of reach, a disadvantage that became more decisive in the jet age even though useful fast ships such as Vanguard remained in service for a time.