A lot of tasks can be parallelized if you think hard enough. Your CPU is busy reordering instructions so they keep as many execution ports busy as it can so that it can retire as many instructions per core cycle as possible. SMT was invented to keep those execution units busy by running more than one instruction stream at a time.

The incentive to do it when most computers have two SMT2 cores is small, but as the average device starts getting 4 or 8 SMT2 cores, or 8 asymmetric cores, the incentives to make things run faster in parallel get better and better.