Putin is acting like a typical Russian leader, they never react immediately. There's an old saying about the Russians taking a long time to get on the horse but once they do, their charge is unstoppable. Putin also is known for getting revenge long after the slight that was made against him. It's not "hesitation" due to the reasons that author seems to believe. There's always another layer to Putin's game. It took the Russians years to come to Syria's aid, but since they did, they've been devastating.
There's some unconfirmed crap I've seen claiming that Turkey and Russia agreed to set up a "demilitarized zone" around Idlib. This claim is not supported in any Russian, Syrian, or Iranian news media or by any named Russian or Turkish official that I could find.
Idlib is being surrounded and cut-off. The Russians, Iranians, and Syrians are doing what they've done before; surround, lay seige, gradually tighten the noose for about 2 months - then smash the hell of the place when they're good and ready. They've asked the last terrorists groups to surrender, knowing that they won't. This gives them a pretext for comes next. Since the terrorists won't surrender, the next step is when special forces units go from building to building, block to block, killing everyone that looks even slightly like a muslim fanatic. They've done this before. They'll leave none alive except the civilians they find. They've become very good at this.