Earlier quoted context omitted.
Well, presumably that's because of a lack of our ability to determine viral markers that identify spread with high certainty. If we could simply determine who we contracted COVID-19 from, we could easily sue them for damages and then you could take whatever risks you deem acceptable. However, considering that we cannot, there is some threshold level of danger above which society will deem your personal rights forfeit…
What gives you the idea that you are entitled to sue someone from whom you have determined that you have contracted covid-19? And do you think you have this right only regarding this disease, or other similar diseases as well?
My rationale for this case is quite simple. I have very effective protocol around this disease, high risk tolerance, and I want to retain the life I had before (going out, restaurants, clubs, etc.). In exchange, I'm willing to allow you to sue me if I get you sick. I think this will create a freer society, and allow people to find their own position on the risk-benefit curve. It doesn't make sense to subject me to the conditions less-risk-tolerant people want. However, it doesn't make sense for me to subject them non-consensually to conditions I want. A good mechanism to balance these things is a near-continuous universal value measure. A good near-continuous universal value measure is money.
FWIW I've rewritten your question from "why do you feel you are entitled to sue..." to "why do you think it is a good idea for society to permit people to sue..." since I think that's more interesting. The answer to "what gives you the idea that you are entitled to sue" is "nothing, since I do not believe I can right now" which is sort of a boring (though correct) response.
Of course the whole thing is moot. Hard to prove who really caused an infection when community transmission is rampant.