But the fiat currency transactions are slow and extremely costly especially when the transfers are meant to cross borders

Let's even forget cross-border transactions for a second and look at the transaction fees our Banks charge us for sending certain amounts to even people using the same bank as us. How about even MoMo transactions. It's funny when you look at a concept like Hive - lightning-fast & feeless transaction. In my opinion, in today's world, the people who heavily depend on only systems like banks either do not know about crypto or are just too rich to care.