Inclined armor follows the expected battle

Why did some British capital ships use inclined armor while later designs did not?

The choice followed the expected operational role: inclined armor suited a ship expected to trade fire in the battle line, while running engagements favored other arrangements.

Designers begin with the battles a ship is expected to fight and shape the protection system around those threat angles. Inclined belts make sense for prolonged battle-line exchanges, but a ship designed for different engagement geometry may spend its displacement elsewhere.