BTC network difficulty decreasing, why?

This is something that happens every 2,016 mined blocks. The difficulty is adjusted according to the Hash Rate of the network in order to keep the average of one mined block every 10 minutes. Nothing alarming here.

The important thing is to step back and see that over a longer period of time, the difficulty to mine the next block keeps increasing. This implies that the security of the Bitcoin network is getting stronger.