Why the frequent requests for IC number?

I was at FairPrice recently and was prompted to register for an account, which required my identity card number.

When I made a mistake in typing it, I was prompted to re-enter it. This seems to indicate a link to a central database.

In view of the Personal Data Protection Act, is it good practice for even a grocer to have access to my data? Surely, my mobile phone number would be good enough?

I frequently encounter requests for my IC number, even when booking tickets for a concert.

This is perplexing and worrisome, in view of today's ease of hacking.

Brian Quek Jian Liang