The reason is that no one buys with bank deposit, including myself.
When I first got into bitcoin it was a nightmare to get coins and it still is. The problem as I see it is that people dont know who to trust.
The development of third party institutions to trade came forth as a necessary addition as civilizations grew. Humanity had grown to the point where people no longer knew the reputation of the people they were dealing with. In early human civilization reputation was knowable because you traded regionally, as populations grew the desire trade across boarders with individuals of unknown character grew with it. The answer was institutions. I dont trust you but I trust them, and that is how things have progressed. Third parties have thrived to the point that they control every aspect of wealth and wealth transfer including the minting of money.
The problem is people have their own money issued by the people for the people (bitcoin), but no one knows who to trust we have all become to reliant of these institutions. So the thing that is lacking in our new economy is feedback/reputation. Thankfully we have a technology that has the ability to to keep track of the reputation of every man woman and child on the planet. For the new economy to thrive and work it requires two things, 1) a bridge between the old banking system and the new and 2) a reputation center to manage it.
So the reason that I trade for reversible methods is to help provide that bridge and build that reputation center. Bitcoin will never have wide spread acceptance if people can not quickly and easily get them.
Your very first sentence is incorrect. You stated that nobody buys with bank deposit. Every transaction that I handle is handled in this exact manner without any issue whatsoever. Both the buyer and the seller feel it is the easiest, and in the process, it is non-reversible.