I don't think a lack of imagination is at question here, but that you aren't given any tools to craft your own background. Currently you can choose race, sex, class, and a generic occupation (straight out of the handbook) which is little more than a way to Tag! skill proficiencies. Unless you're talking about making head-cannon backgrounds for your custom mc, which I consider akin to playing D&D without rules or dice rolls, it can be fun, but without any feedback from an impartial third-party, It ends up just feeling a little shallow.
The head canon background would be using the DnD rules which are very open when it comes to this. I haven't played with a DM who expects the background to be randomized with dice rolls unless I have misinterpreted you? I come up with backstory using the DnD rules and the proper world setting, and there is only discussion if there is to be any homebrew stuff in there. My character then develops as the game progresses according to things that happen, this part I do in any rp game.
I guess a specific example is in homebrew (sometimes even in premade modules, depending on the DM), the DM can often incorporate part of your background into the story. Find your lost lover, avenge your parents, reclaim your birthright, introduction of an NPC that is from your background, etc. This greatly helps me, at least, to rp my character and feel like they're a real part in the world.
Obviously, I don't expect BG3 to have this type of thing due to the vast amount of work/permutations it'd require. But there's some happy middle ground between headcannon-only Tav and ^.
Of course, Larian could already plan to do something like this in Act 2, in which case great! ^_^