I believe it makes sence ...
Narratively:
That guy with no armor, who is holding back ... is logicaly either spellcaster, and therefore dangerous ... or civilist and therefore easy target.
Mechanically:
He have lowest AC > therefore attacking him have bigest chance to success.

But i get it ... i was also kinda dissapointed when i find out that my Dwarf Shieldmaiden Fighter is not as tanky as i expected. :-/
But there still are ways to force enemies to fight your tank ... one of them, even if kinda cheesy, is save your Bonus Actions and hide your ranged dps at end of their turn ... i know it dont work for first round, but after that its like a charm. (Unless you are direcly on sight ofcourse

)
