It's simple in my opinion because 100% population in the world are directly connected with finances, but 100% peoples aren't directly connected with other sectors. We can't imagine our life without money, so when a blockchain application built financially based then they become more popular easily. But other sectors like education if built blockchain application then it will be limited to the teachers & students.

More importantly, blockchain becomes most popular by bitcoin which is financially related. That's how financial blockchain applications become popular.