Why is conventional galvanize obsolete?

Any time anything replaces anything else, it makes the old thing no longer necessary.  If you only need a light coating of zinc on a strip (with InterCoat®ChemGuard), then why would you ever use heavy zinc coating?  If the corrosion protection is much better, and much cheaper, and uses dramatically less zinc, the old method is out of date, obsolete.  Every technological change brings obsolescence, or it isn’t much of a change.  A standard practice is replaced by a new standard practice, because it is better or less expensive or more efficient or a clearly superior method.  InterCoat®ChemGuard is all of that.

If you are still applying heavy weight zinc coatings (above G30 for HDG), if you are buying or selling heavy zinc coatings, if you are manufacturing products using heavy zinc coatings, you are using an obsolete technology.  Until now there was no choice; to obtain satisfactory corrosion protection you had to add zinc.

That is no longer the case.