With centralized institutions such as payment processors and banks, relatively perfect data on usage statistics can be easily obtainable. With decentralized payments systems such as Dash, however, publicly available transaction data can be highly misleading, as anyone can send any amount to anyone, anywhere, and at any time, for whatever reason, and incur only trivial costs of a fraction of a cent per transaction. Additionally, since many cryptocurrency transactions are speculative, a high degree of traffic may be simply moving funds on and off, or across, exchanges, or shuffling personal funds into various storage options. Finally, because barriers to sending transactions are so low, writing a script to simply broadcast various transactions across the network is fairly easy and extremely inexpensive, further complicating the validity of transaction data when estimating real-world purchases.
Read more here