defining the operational semantics of a concurrent language
Coinductive Big-Step Semantics for Concurrency by Tarmo Uustalu writes:


  Second, contrary to what is so often stated, concurrency is
  not inherently small-step, or at least not more inherently 
  than any kind of effect produced incrementally during a 
  program’s run (e.g.,  interactive output).  Big-step semantics 
  for concurrency can be built by borrowing the suitable 
  denotational machinery, except that we do not want to use 
  domains and fixpoints to deal with partiality, but 
  coinductively defined sets and corecursion.


So the answer is that it is stated throughout the literature, but it is not true.