It has to to with the history. The queer community hasn't always been as connected as it is today, and with identity being connected to these terms it's more unifying to be inclusive for gay men and lesbian women, two historically separate communities doing separate acts of activism existing in tandem.
It's LGBTQIA+ because it encompasses each subset of whatever that person feels they fit into. Someone who is intersex isn't inherently gay. Someone who is asexual isn't gay at all. Someone who is questioning doesn't know what gay they may be if they are at all.
Q+ would just be queer+ which doesn't necessarily dignify the history and its significance in how queer people are more accepted in society because of the riots and protests.
Lesbian, gay, bisexual, trans people all fought and died so that younger queers could stand a chance at being accepted for who they are today. It seems only right to continue to honor that despite something as petty as it being "unoptimal".