Why is LGBTQ all together?

As regards the T, a lot of T people are homosexual or bisexual (ie transwomen attracted to women and transmen attracted to men). With those that aren't, they are still often labelled as gay by others and receive the same discrimination that gay people often get - it's not unusual for people to call trans people "super gay", or "gays in denial" or "gay people trying to trick straight people". While these labels are inaccurate, that does not stop the homophobic abuse trans people receive. This is the common cause between them. It's not that T is an expression of sexual identity, it's that T people often get abuse from others similar to that which LGB people receive.

Q is generally for people who don't fit nicely into any of the other brackets but are still subject to homophobic abuse due to not fitting gender and sexual norms.