Because you can have it and be spreading it without showing ANY symptoms. And if you test every 3 or 4 days at least you would know just how long you have likely had it and possibly have been spreading it, therefore making it easier to check who you have been in contact with who you may have given it to. At least once you do show positive you can isolate yourself at home until you have 2 negative results, rather than walking around spreading it to others due to your being ignorant of even having it. Seems the responsible thing to do, especially if you have a lot of contact with the general public. Bangkok and Pattaya have higher numbers than up here in Surin, where, at the moment, we seem to have around on average 70/75 infections daily (where just 2 or 3 weeks ago we were finally under 10 a day). BKK being almost 800 daily now, and I expect Pattaya's numbers also to be higher than ours are here.