It's because despiste Campitor explaining how it worked, some stupid people insisted in saying that it would automatically upgrade the item to +8/+9/+10.
This system is actually much better than using HD ores only. Try spending 1b in HD ores to have your +7 item back at +3 and you'll love BSBs.
now we will be able to spend 1b in HD ores and 500m in BSBs to have our +7 item still at +7 lol