bitcoin is absolutely the fastest way of transaction, if anyone want to transaction abroad.bitcoin could also minimize time duration and also other troubles that are commonly happened during withdraw money.but for making that process, sender and receiver both need to have btc wallet address.truly btc already has enough fame in worldwide but i can assume that most of people still don't know the process of use bitcoin and where to store it.so they select 3/4 days delay preocess, that's the simplicity of them.
I don't agree with the part you said bitcoin is the fastest, I think alot of people will say the same thing too, transactions done with bitcoin are not the fastest, for faster transactions you can use coins like xrp or trx, but that shouldn't be the reason people avoid bitcoin, for me I think due to the little or no knowledge they have about bitcoin is the main reason why people tend to avoid using bitcoin for transactions, people will always avoid what they have no idea about, but I think it's up to us to educate about bitcoin and tell them the benefits of using it.