Because the virus is triggered by stress. If your environment is dialed in and your plants are stress free, it's very likely that the virus will remain dormant or not be a major issue.
If your plants are healthy it doesnt show the symptoms but its still there and will still infect other plants, silicone for instance will mask the symptoms.
As far as i know its uncurable and physan 20 will not cure it nor will taking cuttings from the top of the plant the virus is systematic.
I have this shit in my garden and it spreads easy espacially if there are thrips about...everything needs to be sanitized not sterilised..im about ready to burn all my tents when the next few gardens finish up!