People used to think this card wasn't very good.
In that context...it was generally terrible, because it goes away as soon as you steal an agenda. If the corp brazenly installs and starts scoring a 5/3, you still couldn't touch it without losing the protection you had. And it never served any purpose against the other popular kill-enabler, Midseason Replacements.
Put simply, installing NACH telegraphed in big neon letters "I AM NOT GOING TO RUN FOR A WHILE" giving the corp free reign to score out at their leisure. The only runner who could make this work was Iain Stirling, who was basically okay with turtleing up and waiting for a good moment to strike. For everyone else, a card which hindered your ability to do the very thing you need to do to win the game--that is, steal agendas--wasn't worth playing over the more reliable counterpart Plascrete Carapace.
But the meta has changed, in two fundamental ways. The first is the introduction of Film Critic. Film Critic allows you to take agendas without "stealing" them. This already helps prevent kills by neutering Midseason Replacements, Punitive Counterstrike, Argus Security, Personal Evolution, and other tactics. With NACH, it can go one further, preventing you from losing your anti-tag measures.
The second is the whole mess of new tagging options available to corps as a result of Data and Destiny. In particular, the appearance of a new kill strategy, 24/7 News Cycle+Breaking News, meant that you can no longer avoid the kill by not running and hoarding credits, while SYNC makes it extremely expensive to clear tags from Data Raven, Gutenberg, or News Team. Strategies are now emerging which use tags for things other than simple murder--cards like Quantum Predictive Model, Keegan Lane, and The All-Seeing I hurt you in devastating, potentially game-ending ways, where Plascrete Carapace isn't going to help.
This means that it is no longer enough to simply run early and clear tags afterwards. You have to actively prevent the tags from ever happening in the first place. And that is where New Angeles City Hall comes in. As long as you have money to burn and Film Critic to help you steal, you will never have to take a tag. And that is a wonderful, wonderful thing.