Most D&D characters never reach anywhere near level 20 during their entire lifetime. Baldurs Gate 3 is just one campaign lasting a few months at best.
High levels are very difficult to do right. How should the world react to a mage who can Meteor Swarm a city or Wish it into mushrooms? How many world ending threats and ancient dragons can there be?
Baldurs Gate 1&2 had pretty perfect level progression with BG1 taking you up to ~9 and the sequel going all the way to epic.
More doesn't equal better. 12 is a lot already.
