Decline in cryptocurrency markets is probably due to loose ends of security and accountability. It best suits Whales and manipulators where small investors are eaten up easily. Though small but these investors accumulate billions of dollars across the globe. Being small investors they are at the mercy of manipulators. The perpetual loss has led to shattering the confidence thus market declines.
Most of the countries are now enforcing tangible laws to protect their people investment which also led to slowing the market.