The core word here is mistakes. No one knows what the right way to react to a international crisis is (though the argument for complete military non-interventionism gets stronger every time a military intervention just makes things worse...).
You have to distinguish between decisions made in good faith that backfire (or perhaps the alternative would have been even worse?), and malicious decisions like what Trump is doing
How did Obama make that decision not to follow his promise on crossing "red line" by Assad? What were the pros and cons for that decision? How can we be sure that it were not purely U.S. internal politics arguments for giving up? Questions like that do not allow us to forgive mistakes: they force us to hold the governments to account.
And questions like that are asked and answered? Obama had good reasons for not following up on that threat. Read, for example, theatlantic's 'Obama Doctrine' article. It was never obvious that a heavier US intervention in Syria would help the people in Syria at all - in fact, history suggests that the opposite.
On the other hand, it's hard to imagine how the US refusing refugees would make the Syrian situation worse.
How not? Just the fact that it made news in outlets like nytimes and guardian means that people did care and feel outraged. Things that people don't care about aren't read.
But you're correct the outrage wasn't aimed at Obama. Why? Because there's a difference between a president that acknowledges there's complexities to immigration and refugees, and works on a compromise, and one that seems to treat anyone from the Middle East as of no moral value.
Drone strikes stats can be seen at https://www.thebureauinvestigates.com/category/projects/dron...
I can think of several reasons. I don't necessarily think they are all good reasons.
1) U.S. bombings are seen as a good-faith effort to stop terrorism, based on intel etc.
The current executive order seems more like a rash decision based on xenophobia and poorly implemented (in the early hours, border officials were giving confused and contradictory info on whether green card holders were affected, etc.)
2) The collateral damage from the bombings, added up over a decade, has probably been hundreds of innocent civilians' lives in some of these countries. This is upsetting but distant.
On the other hand, the collateral damage from this executive order is that 500,000 expats living in the US can't leave the country, or are stranded outside the country. For American "coastal elites", myself included, these are not remote people but our friends, coworkers, professors. Everyone in my social circle seem to have at least a second-degree connection to someone from Iran.
3) The current executive order threatens the standing of the communities "coastal elites" are part of: top American universities, Silicon Valley, the medical community, etc. These institutions are world-class due in no small part to how welcoming they are to foreign talent. That could change if the smartest around the world start heading to universities, hospitals, and companies in Canada or Germany instead...