It is that way to cut down on the amount of players that would actually bot this. If everything is bound to account then it narrows down exploiting. Make the items free trade, would kill the market on some items like Legendary Hammers but also open the way for forms of botting.
However, if you set that to something that is already unlimited like Celestial Basin and Moon Refuge then you would basically kill those areas off for those players who want to farm it for experience charms, moonlight bud for alts, awakening skybreak items, min/maxing fallen / ivory soul shields, limit the amount of hammers they could buy a day, or HM1-15 1mil experience charms which all help them catch up in a manner of speaking. Grant it most of that people consider old content crap but as a new player its 'new content'. And yea, I get it they could have the monsters give more experience, moonlight bud to drop off them and so on but I highly doubt any of this will come to be.
Ok, say you make it for only 1 person to enter then it automatically closes. Why have a special zone at all in that regard when they could have what drops inside drop off the monsters outside and save resources coding wise and server wise. So what is the pro of having it aside from helping "that" player in getting some materials.
Everything sure does but long story short this is a Korean game. So we honestly have very little say on how things go. I mean I would honestly love for them to just give us the Korean game client with only 1 change language based on region. No other changes. Won't ever happen but one can dream @Hime