Why does he only want answers from his supporters? Is he not the president of the entire United States?
He's also the leader of a self-defined movement to uproot the status quo of the USA. Now, whether he
should be a leader of such a movement and whether or not it creates a conflict of interest with his presidency are interesting questions, but ones that were clearly disregarded when this survey was produced. Both in the e-mail and the survey, he quite clearly addresses the "people" behind that movement. There should be a time and place to listen to opponents, but it doesn't have to always be the case.
And even if it were a poll for his supporters only, the questions are still loaded with assumptions about the media.
The phrasing of the questions is far from ideal, but most of the "loaded" questions are along the lines of "do you agree with this statement?" They're clearly there to compare and contrast the sentiment of the MAGA movement's leadership and its core supporters.
So what exactly is the point?
Probably to figure out whether or not his core supporter base agrees with the recent developments of his movement. That his opponents still violently oppose him is obvious and largely immutable. Whether or not his current supporter base is having second thoughts is something worth looking into.
Not listening to your supporters is an easy mistake to make, and one that costs political careers. Just look at the Labour Party in the UK, or the Democratic Party in the USA.