If you look at it as Currency, it is difficult for an average person to understand it because it is different.
Bitcoin, being a different kind of a digital currency, it breaks down conventional thinking in many aspects. No central regulatory body. The concept of mining. The open-ledger (blockchain), the way miners are rewarded, how transporting value is determined by its packet size and not value, the hash rate, the concept of limited supply. The 100 Million pennies in a Bitcoin, etc.
Its difficult enough for people in the money space to thoroughly understand Bitcoin (we all say we understand it, but do we really?).
For a common person, its an overkill. Its like trying to explain the concept of TCP/IP, Networking, Routing, the Internet for someone who wants to use email. Overkill.
Because bitcoin is something new that people are not used to. It takes time for people the grasp the meaning and significance of it. But you don't have to totally understand the difficult technicalities behind to get involved with cryptocurrency. A basic research would help a beginner to start his way up.
Some people are having difficulties in understanding bitcoin and cryptocurrency because they are not willing to take some time to study it and take a look at it. At first, I also have some confusions about this bitcoin and how it works, but because I am very interested to know more, so I take some time to do research and little by little, I already understand it. So for them who dont understand what bitcoin is yet, they just have to be open-minded and do some research like in google, youtube and sources like the bitcointalk forum.