The government can't just take away all your cash on a whim without any notice. That's why, I guess, some people prefer cash. If you want to use cash, you want local shops to accept cash. Personally, I'm OK with being cashless.
The goal was to "make illegal money" (i.e. tax evasion / sourced from corruption) useless.
https://en.wikipedia.org/wiki/2016_Indian_banknote_demonetis...