Why did landing craft keep getting larger?

Why did landing-craft designs become progressively larger instead of staying small and flexible?

Some craft rode aboard landing ships, while others needed to transport themselves and heavier payloads; the latter required larger hulls.

The smallest hull did not always offer the greatest flexibility. Craft carried by landing ships could remain compact, while self-deploying types needed more range, capacity, seaworthiness, and room for weapons. These were parallel design strands serving different parts of an amphibious operation.