My understanding about SARS (disclaimer: not an epidemiologist but I did live through SARS in Singapore) is that as Po says the lack of asymptomatic transmission was key. But the high case mortality rate (10-11%) was also a factor in it being able to be controlled — the virus basically burned itself out. My feeling is that Covid is insidious in that the asymptomatic transmission makes it hard to find, and the 1% death rate is dangerous enough to lock things down but not enough to really scare people or burn itself out. But as I said, I’m no expert! I do remember though that despite SARS being 10x as deadly, my life was much less impacted in Singapore than it is now!