No one knows that, at least not until after the fact. All everyone knows at the time is that the duke is a bigoted jackass who will jump on anything in order to further the goals of Weaseltown. The fact that the one subject from the princesses' kingdom keeps saying that on purpose, means that it must be patently obvious to all the political guests as to why he won't shut up, because no one likes them because frugal merchant nonsense and he's clearly jockeying for some personal gain, which is later revealed to be assassination because he didn't want trade to stop. Assassination is a big deal and that's plenty reason for them to evict him. It would also likely heavily damage their image in the eyes of the other nations who were witness.
1. If no one knew until afterwards that the Duke tried to assassinate Elsa, you can't exactly use that as an excuse for them not reacting before. Which is what you did.
2. Again, how would they find out after-the-fact? Yes, the Duke's men ran ahead and tried to shoot Elsa. No, there wasn't anyone who could confirm anything unusual about this. Elsa never got a chance to find out that the others in the party wouldn't kill her, except Hans, and a 2:1 ratio of "tries to kill me:tries to capture me" isn't enough to make her suspect the two that tried to kill her. No one in the party was there for the two trying to kill Elsa--they showed up when Elsa was trying to kill
them, which makes the one aggressive act they see (the soldier pinned to the wall trying to shoot Elsa) more or less justified. Running ahead wouldn't be suspicious, either--the sooner they could get to Elsa, the sooner (one hopes) that the giant snowman stops attacking them. (Not that crossbows were doing anything to it.) Oh, and how many people there do you think knew that the men were the Duke's? Certainly not Elsa, and since she's the only one who knew they tried to shoot first...Not that any of this matters, because no one who wasn't there is likely to get any information on the attack. Certainly not information that's similar enough to what actually happened to matter.
That's a good point. Obviously all the subjects of the kingdom would be biased towards their princess, but the political guests were still in attendance and were also all universally wowed and enjoying the trick, wouldn't you say?
What makes you say the political guests were still there? Kinda illogical. Once the roads and seas were clear...the coronation was over, the hostess was a scary ice witch, and a scene or two before the ice skating we see the Duke and other political guests getting onto their ships and leaving.
Before hearing that trade was cut off, for the Duke. (Good timing.)
So people can't complain? And so you don't have to waste your time with justification? And so you can have complete artistic freedom? There's literally every reason to say so, even though it's pretty much already been established unless a Frozen 2 comes out anytime soon to effectively nail that in place.
On the other hand, it's my time I'm wasting, my artistic freedom I'm
constraining, and anyways I've given the matter far too much thought already so I might as well use it all.
And people can complain. Complain away. If you care that it doesn't match with your vision of what happened during Frozen, I'm perfectly willing to defend my interpretation.
1 was clearly a jerk (Duke of Wesselton) but the other I can see being sympathized with.. Sort of? He kinda was being obviously manipulative, what with locking up the princess-sorceror and trying to marry her sister for obviously political reasons, which, while perhaps not unusual during medieval times IRL, definitely was considered disgusting and an act of deception in this universe. And usually an arranged marriage is, well, arranged, and involves mutual gain for the two sides with regards to relations and lineage. This was not the case here.
By the way, they weren't technically engaged. If this is back in the day then engagement requires ceremony for it to be formal.
Interesting fact. Of course, two things.
1. Anna and Hans told Elsa they were engaged. Either this requirement doesn't exist (which is an assumption I'd rather not make, for several reasons--chief among them being that it's a boring assumption), they performed the ceremony at some point (more or less the way Hans claimed they performed their marriage after Anna "died," and hence evidently an acceptable (though probably frowned-upon) way to performing the ceremony), or Anna somehow didn't know and Hans played off this knowledge, expecting that
no one would fact-check this little detail ("So, how was the engagement ceremony?" "Wait, what?"). The first, as noted, is a boring assumption and has other issues; the last is out-of-character for Hans due to how easily the lie could fall apart and how little he gains; the second is plausible and interesting.