Check out the site which tells the why as below, and more! It matters, including for all straight allies:

“The census tells the story of who we are as a nation, and that includes LGBT people — but only when we participate, and only when we’re fully counted. Thanks to the collection of unmarried partner data, a more complete picture of who we are has emerged. For example, we know that:

• Same-sex couples live in 99% of all US Counties.
• LGBT parents live in 97% of all US Counties.
• Black and Latino same-sex couples are raising children at almost the same rates as their heterosexual peers, but on lower incomes ($10,000/yr less).

Still, there is no question on the 2010 census that asks individuals if they are lesbian, gay, bisexual or transgender — and LGBT questions are not included in almost all other major federal surveys.

It’s a big problem. The census, which counts everyone living in the United States every ten years, provides the data that is used to determine funding and policy priorities at the national and state level.

Being counted isn’t just a numbers game, but a question of whether the LGBT community gets access to the resources that support our health, economic well-being, safety and families. The LGBT community must be visible—and that means participating in the census, but it also means being counted fully.

That’s why the National Gay and Lesbian Task Force, together with CREDO Action, has launched Queer the Census. We must ensure that LGBT people are accurately counted in the next census — and we need your help to make it happen. Here’s how:

1. Sign the petition to the right to pledge your support of a census that counts everyone!

2. Get the Queer the Census sticker and use it to seal the back of your census envelope.

3. Spread the word about the Queer the Census campaign.
   

4. Make a contribution to support the campaign.

Thank you so much for your efforts to help Queer the Census and ensure that everyone is counted!”