Why the heck Strava has so low GPS accuracy...

Hi ​@Pranil, the gps accuracy depends mainly on the device (rather than application), and on the environment. 

For accurate gps, you need skies visibility - if in a thick forest or among very high buildings/skyscrapers, or e.g. in a tunnel, your device won't be able to get the location from the satellites well. I’ve noticed that even a very thick layer of clouds sometimes impacts the accuracy.

Sports watches are generally more accurate than phones, because when the app (e.g. Strava) runs on the background in a phone that's in your pocket or backpack, the location may not refresh that often - and the phone also doesn't have a clear view of the skies. Sports watches (Apple Watch, Garmin etc) are performing much better - and if you're considering getting one, make sure to buy a watch with a multi-band gps (the recent models usually have it).