Let me walk you through my logic on this and maybe we can stop with the condescending entitlement argument, mkay?
Because the purpose of the K-1 is first, to provide a path into the country, and second, to provide a path,
if the conditions, viz. marriage to the petitioner are fulfilled, for adjustment of status. And it is NOT essentially an immigrant visa. It's essentially a non-immigrant one. If you don't marry within the 90 days, you either have to leave, just like a tourist visa, or on the assumption you've married late, file an I-130 because you are out-of-status on a non-immigrant visa.
It's the marriage that does all the work in getting permanent residency. The K-1 just gets you here (useful if you're from a country where you can't get a tourist visa) and gives you 90 days to play with. It's like a tourist visa for a purpose, and doing it means you eliminate one form and maybe get the medical taken care of.
So, given those two conditions, what does making a person from a VWP country (or here on a student visa, etc.) file a K-1 accomplish? Reduction in fraud? On the contrary, the countries are on the VWP list because they are already low fraud, and if someone wanted to come here and stay, they'd just hop on an airplane and stay. No need to swindle an American into a green card. At least not ahead of time.

Protection against disease? We assume the people are fine to visit for a 90-day VWP stay; if they file for AOS they need a medical at which point diseases would be caught. Net protection against disease by making a VWP person go through the K-1 = 0. Protection against terrorists? Again, VWP. If we're not worried about terrorism enough to kill the VWP, it surely doesn't do anything to add a fiance interview of three minutes into the process.
So we can conclude it has nothing to do with keeping undesirables out of the country, when the applicant is from a VWP country. If they just wanted to get in, they'd already be here. And if we are that worried, we should make everyone apply for a tourist visa.
So all that's left is providing a path for adjustment of status. That's useful, like a headache is useful, but it's really easy to replace with an I-130, as people manage it all the time if they're here for other reasons (work, school, spontaneous weddings) and get married. Construing this as wanting privileges based on country of origin is really rather insulting. It has nothing to do with race or language or whether I like Canadians and everything to do with the fact that the country has already decided that this country is a low fraud risk and lets them in for all sorts of purposes,
even to get married.
There is an awful lot of redundancy in this process. And if you eliminate redundancy, everyone's processing times go up. How much faster would the immigrant visas in Montreal go if they didn't also have to process K-1s? How much faster would it be at the service centers if they didn't have to approve VWP K-1s.