The issue here is not that Melania plagiarized Moochelle's speech. The issue is that the Trump campaign used the same speech writer as the Obama campaign and then lied about Melania writing her own speech.
Not true. The facts are these: Matthew Scully, a speechwriter for George W. Bush, wrote a draft of a speech. It was then given to the Trump campaign. A professional speechwriter would NEVER risk his career by plagiarizing.
So, the Michelle Obama changes were added by the campaign, and most likely by Trump and Melania.
The Trump campaign is too stupid to use anti-plagiarizing software, so Trump's additions got past vetting, and you have what you have now.
Nobody is being fired over this episode because Trump would have to fire himself.