Dealing with shared state is not always easy when you're working with multiple threads. If you can't reasonably avoid that sharing because of the nature of your problem, and if your choice of language and tools only provide tools on the level of manual locking, then I agree that writing correct, thread-safe code has its challenges.

However, there are plenty of scenarios where you don't need much if any state to be shared between threads. That includes almost every example of JS promises or async/await that I've seen this evening while reading this discussion and the examples people are linking to.

There are also plenty of more sophisticated models for co-ordinating threads that do need to interact, from message passing to software transactional memory. These are hardly obscure ideas today, and I don't think anyone could reasonably argue that for example message passing makes things complicated but async/await/promises make things simple.