They don't do it on purpose. It's just really easy to do accidentally with custom allocators, and games tend to use custom allocators for performance reasons.

They don't do it on purpose. It's just really easy to do accidentally with custom allocators, and games tend to use custom allocators for performance reasons. The system malloc will return pointers aligned to the size of the largest Atomic operation by default (16 bytes on x86), and compilers depend on this automatic alignment for correctness. But it's real easy for a custom allocator use a smaller alignment. Maybe the author didn't know, maybe they assumed they would never need the full 16-byte atomics. Maybe the 16-byte atomics weren't added until well after the custom allocator.