Lock free algorithms still use primitives like memory barriers. A memory barrier in a shared memory system is expensive, but not nearly as difficult as a memory barrier in a distributed system.

Additionally, distributed systems not only experience failures of individual components, but they're often in a state where you can't reliably detect failures (e.g., tell a failed node apart from a node that's slow or a node that you can't temporarily talk to while other nodes can).

It's also possible to think of it as a continuum: for example, failure detection is simpler in a distributed system connected via Infiniband than in a system connected via commodity ethernet; locality matters in NUMA CPUs and so on. The idea that a commodity multi-core machine has some properties of distributed system is not without merit, but it isn't particularly useful or actionable as a working model.