Originally Posted by 
JDNSW
				 
			Very simple - the R0 of covid19 is far higher than the three diseases mentioned. In fact, it seems to be higher than any other serious disease except measles. Estimates vary from about 3-6 for covid19, compared to around 12 for measles. It is also infectious before symptoms appear, and an incubation period long enough to allow symptomless patients to do a lot of spreading. And the fact that for many patients, it is not serious, so they don't isolate.
This means that without (effective) control measures the number of cases is going to increase very rapidly to very high numbers. Given the case fatality rate of around 3% (seems to be similar everywhere that has reliable data collection, including Australia), covid19 results in numbers of deaths far greater than diseases such as SARS, MERS and Ebola. SARS has a lower R0, and was easier to control, although it frightened a number of countries, MERS has no confirmed human to human transmission, so R0 is well below 1, and Ebola is not strictly an airborne disease, and is fairly easy to contain in advanced countries where good hygiene is practical.
Then there is the problem of "long covid" - the disease has only been around in significant numbers for about eighteen months. Data is still coming on this, but so far it seems possible that it may affect up to 50% of those who have even very mild cases of covid19. Having known people with post-polio syndrome, and having suffered from shingles (follows chicken pox after many years) myself, I see this is a major concern.