Because it is black and white, since there's a 100-year history that proves that ALL socialist models fail.
You can cover your ears and eyes to pretend that Canadian & UK health systems aren't in crisis right now and will get worse as the population ages. To you and people who think like you, a victory is declared when coverage is miraculously provided to 100% of the population, quality of care be damned. Yet, the Denver Health is a classic example of the consequences. The hospital staffs up for more volume, basic care increases, but acute care gets worse.
The worst part is that the true bad news won't hit for several years, because the hospitals and clinics can still function on equipment and facilities that they've invested in over the last decade. So in this period, everyone will sing happy songs about how great the new universal coverage is and how more people can see a doctor without worrying about the bill.
And then you fast forward a couple of years after the best doctors leave socialized medicine and hospitals slow down their investments, and the old equipment starts breaking down. Suddenly, the next doctor's appointment is in six months and a visit to the specialist is in one year. No problem. You're covered by healthcare.