"immigration bad" is easier to attach scary numbers and stoke up fear.

It's easier to have the media cycle showing bad things immigrants do (which - imo - is likely statistically inline with the general population. But because it was an immigrant that did it, it has extra biases attached), than feel good stories of how immigration helps a country & economy.

The fact that immigration is generally a net positive is hard to describe in soundbites and catchy headlines.

So the right makes scary statements and flashes scary numbers and promises to do something about it. And it's difficult to nail down exactly what they are going to do about it.
And, of course, that single issue party doesn't run the government for the people so you end up with a bunch of bullshit harmful policies being enacted.
It ends up being the message of the policy that drives the news cycle, not the policies themselves.

While more progressive parties talk about equal rights, better taxation, more social services. And everyone talks about money trees or politicises medical issues.
So it's the policy that gets raked over the coals, instead of the message of the policy being the story.

And finally, the majority of news companies are owned/run by right wing (or at least right leaning) millionaires/billionaires.

The common denominator seems to be someone yelling that immigrants are bad.

Absolutely. Immigrants are shaping up to be this century's Jews.

I'm not saying migration isn't an issue at all, because it is,

Really, it pretty much isn't. Immigrants simply highlight issues that already exist, like lack of opportunity, housing shortages and weak social security while ruffling bigots' feathers.

The main reason why the more populist government won this time around over the VVD (the more centrist conservative party) is down to the failures of the VVD in the years before, causing this mess we're currently in, and the fact that the populist candidate slightly softened his rethoric about immigration. Don't get me wrong, he still hates immigrants but he went from wanting to ban Islam and burn Koreans to just wanting to send immigrants back to their own country. On top of that, he also seemingly steered more into being there for the "normal" (read: white) Dutch person.

As for them not getting anything done: this was more or less expected. It's part of the right wing playbook but it's also just such a mess here politically with all the different factions with different goals that cancel each other out that it is very difficult to achieve anything.

Want more houses? Farmers have to give in, leading to massive protests and tractors on the highways. Also, with the farmers party in the government this could cause them to have to resign. Want more farmers? This isn't allowed due to Dutch (and EU) nature laws and regulations (thank God we have those). Want to give money to lower class people? Oh wait, they're right wing... They might promise that to win votes but that will never happen.

At the moment the best we can hope for is that the populist leader comes through on his threats of pulling out of the government if he doesn't get his (crazy) way soon and that the people here have learned their lesson that voting right doesn't achieve anything. I'm sure VVD will still get a lot of votes but I at least hope that we can get a mixed government again, it's been a long time since that happened...