@padmaraj.ravi,

The answer is very simple. The reason is the criminally inefficient use of resources in Sailfish, particularly RAM. You will have people blaming Alien Dalvik (AD) but I have never allowed AD touch my Jolla and still see apps killed at the background.

The biggest change that brought most Out-Of-Memory (OOM) problems was the 1.0.8 update that upgraded Qt. After that, you were lucky to run more than three apps simultaneously, even without AD. For me, it was sometimes enough to run just one(!), the browser. Have two tabs open and try opening the third - bang! The browser gets killed.

To Jolla's credit, the 2.0.0 update fixed a lot of OOM issues. In fact, since 2.0.0 came out, I have seen only one instance of an app killed by OOM.
Others' experiences may vary if they use AD. For them, 2.0.0 may or may not have fixed the problem, or it may have made it worse.