why the webopac should be nopac

Here's the thing.  The OPAC, or the ILS, these are internal inventory management systems.
No one in their right mind tries to use their internal inventory system, designed for experts, as their public interface.

You might say, "but Amazon does this".  So I will tell you a story about Amazon.  It is a fib, but it's short.  I have no idea what Amazon's internal inventory system looks like.  But it certainly COULD look like a green-on-black text terminal where the inventory people enter stuff like

LOC 1231231231 PULL
and it says stuff like

Q30 A10S3L4 R4

that's it.  No fancy graphics, no reviews, no this-is-related.  It's a system to let people find books in a warehouse.  It doesn't need to be any more than that.

Their client-facing system has a completely different set of requirements.

This is how it is put in Panlibus, a blog by some Talis staff

As a community we have to recognise that OPACs are not user-centric. Visitors to the library rarely use them for anything other than specific location information, and the idea that web-enabling OPACs in the current form will extend their reach to a wider audience is flawed.