Because, for example in Canada, there have been 1.4 million total cases of Covid over the last year which has on multiple occasions stretched particularly ICU capacity to the limit. In a much shorter time period we have administered 27.7 million doses of vaccines. We give more doses every 3 days than we had cases in 14 months. Natural immunity is almost negligible compared to vaccination. Getting to herd immunity levels with actual infection will result in hundreds of thousands of deaths and damage our health (and healthcare system) for decades.