Do you have the study where they would have reduced virulence for these reasons? Because reducing the virulence of a virus to such a level that a large part of the population don't even get any symptoms seems odd to say the least.

Also, it's not even clear that COVID-19 is that much more infectious (or at all) than SARS, it seems to me that its explained well enough by so many people brushing it off or not even realizing they have it because it's so much less severe.

Reasons a [malicious|altruistic] actor might do that:

You have the ability to use it to induce fear and therefore behavioral changes. Positive cases are valuable.

Plausible deniability.

Mistakes.

Response.

Testing (as parent pointed out).