Simply put, we have to put a price on carbon, be it through taxes, certificates or other means. Emission of carbon dioxide is an externality that's not being priced properly, if at all, by most current systems. This is called "Market failure" and most economic theories call for regulations here... and most big companies who would lose money disagree with that, and we all know where that usually goes...
We did something like that in the EU, and it failed massively, the price for a ton of CO² is completely at the bottom. A bunch of reasons for that, among them the fact that the potential to reduce emissions was vastly underestimated.
The comment in the image reads that the value of CO2 certificates was close to 0 because they could not be carried over into the next phase.
That extremely steep drop in the middle of the first phase was, if I remember well, because some knobhead in the regulation office said "Well, there is way too many certificates currently anyway, haha" during an interview as an aside.
Another thing that was outrageous about how the EU handled this: They gave certificates away via grandfathering. e.g. "You emitted 1000 tons of CO2 last year, so this year you'll get certificates for 1000 tons. But it will be less next year." Not only did this create all sorts of conflicts of interest, but the companies, shockingly, priced the certificates into their products. Means they raised the prices as if they had paid for those certificates when they hadn't.
My take is that it's extremely important to put a price on carbon, and certificates are a great way of doing so if done right.
