the reason why bitcoin can return to a bull run is because many countries legalize bitcoin as a legitimate financial transaction tool, then some positive news about bitcoin and crypto currency trading in various exchangers, and that good news will affect bitcoin for a bull run.
It is essential that we have as many countries as possible to legalize it so that world as a whole can accept it and transaction across the world happens majorly through crypto currency. This can help crypto to grow much quicker and can be used in our daily lives too.
There is always a rise and recovery in the economy. At times, there might be a prolonged stagnation and a fall but since we have the cyclical models, the market is expected to repeat the boom period over again and so on.
Hence, this is the reason that we might experience a bull run. The blockchain is being introduced in many countries and this is the start of digitization of their currency.