We can't blame people in not using Bitcoin or any other cryptos but I am thinking a reason of
1. They are too young/old to get interested with this.(not with all cases)
Bitcoin and blockchain technology is knowledge based and so it's no doubt going to be a puzzle for very young people and most elderly people are of the idea that, it is past their time and information technology seems to be cruising at an intimidating rate that catching seems almost impossible.
2. They have no internet or computer (This is reality)
What should one expect, when a good number of people in some part of the world are living on less than $1 a day! No doubts those would rather step on computers and jump at food, it's such an odd world!
3. They are contented in FIAT currency
Fiats they can see and touch and the idea that cryptocurrencies are "zeros and one" representing money can be scary to people not well informed or people not open to new ideas.
4. They have no money to get some Bitcoin
Same as 2. above, inequalities exist everywhere and life is some struggle.
5. They are afraid because it is not tangible and reliable
Bitcoin is the millennial invention so expect the target market about it
Same as 3., the internet is synonymous with fraud and for good reason, most people remain skeptical of online transactions. Who do they go to, should something go wrong?