The problem with the exclude option in the JD is that it is specific per item. It excludes one specific item in your inventory. It doesn't exclude every single item you'll ever get of that type. If you have to use that, before you use sell all then you're essentially doing the exact same thing as manually selling. Only now you also have to press a "sell all" button afterwards.
Regarding the shop, you have to understand how economy works. Certain junk are needed for certain recipes and since all that is loot, shortages or abundances of junk types dictate prices etc etc. If you just drop them all in a shop, you remove that element entirely and messes up the entire system.
For casuals, it makes even more sense not to use a "sell all". You're essentially selling stuff that are worth eg 15k for 1k credits and stuff that are maybe 1-5k per piece, depending on shortage, for 50-100 credits per piece. Your total loot could be worth 50k and you'll get get 3-5k out of it, to put it into perspective. How does that help a casual player who doesn't have countless hours available to farm? Don't have a vendor? Put it on the bazaar. Ask on discord. RE crafters buy them in bulk and most often have a vendor you can just go and offer all of it and get your cash fast.
The main issue here though is that while it is your prerogative to opt-in to sell 50k worth of loot for 3k, the majority of newbies will not see it that way. They will assume "sell all" sells all your "vendor trash" and, like I said earlier, when they figure out they've been selling loot for pennies, for days, they will most certainly not be happy and will be asking why "sell all" sells valuable loot to begin with. Not to mention this will also create shortages in the junk market as well which, as I understand, is already short on junk loot.