From my understanding he used the same list for the same reasons from when the list was created by Obama's DHS; security concerns.

It's relevant because it means that all the people pointing to the choice of countries as proof that Trump is a racist, doesn't really care about national security, is driven by his own commercial interests, etc are talking nonsense - and most likely partisan nonsense at that, since the list comes from the previous administration's border policy. In particular, anyone who claims that only a racist would think those countries are high-risk and uses this to point fingers at Trump rather than Obama is on dubious ground because it's Obama's administration that decided people from those countries were high-risk. Also, bear in mind that this is ostensibly a temporary thing while they come up with a more suitable permanent policy.

There are, of course, reasons why the countries on that list were there in the first place too - mainly recent terrorist attacks in Europe by people from said countries. I imagine it's not quite the list Trump's administration would draw up (there's talk of adding Pakistan, which is an obvious omission), but given how much flack and dubious accusations they received for literally copying Obama's list it was probably politically unwise for them to create their own.