Why didn't EPA adminstrator Lisa P. Jackson fulfill "high hopes of sweeping action to address climate change"?

Maybe you can find clues in the NYT article about her departure. I note:

After his re-election, and a campaign in which global warming was barely mentioned by either candidate, Mr. Obama said that his first priority would be jobs and the economy and that he intended only to foster a “conversation” on climate change in the coming months....

In political rhetoric, "conversation" usually means: I don't want to talk about it.

After Republicans took control of the House in 2010, Ms. Jackson became a favored target of the new Republican majority’s aversion to what it termed “job-killing regulations.” One coal industry official accused her of waging “regulatory jihad,” and she was summoned to testify before hostile House committees dozens of times in 2011. She was frequently subjected to harsh questioning that at times bordered on the disrespectful.

Ms. Jackson, the first African-American to head the E.P.A....

Oh! Those terrible Republicans! Harshly questioning an African-American! Why it bordered on the disrespectful. At times.

Among Jackson's modest achievements (which appear to be limited mostly by President Obama's re-election-conscious decisions):

[N]ew vehicle standards will eliminate billions of tons of carbon dioxide emissions and double the fuel efficiency of the American light-duty transportation fleet over the next decade.

Billions of tons over a decade? Did you know human beings on earth exhale about 3 billion tons of carbon dioxide a year?

The NYT article ends with this quote from Jackson: "Before me... some people said that African-Americans don’t care about the environment. I don’t think that will ever be the case again." Ironically, that's the first time I've ever heard that stereotype.

ADDED: I was surprised to read that the EPA has 17,000 employees. What's the carbon footprint of an agency with 17,000 employees?