Because of the change in government in Afghanistan their capabilities have enhanced, simple. Pretty sure this was being said since the fall of Kabul that this would happen, just search here on PDF and you'll see threads where this was being said.
TTP now has a base where it can operate untouched, contrary to popular belief US Drone strikes were critical in making sure the TTP kept themselves sheltered, instead they now operate openly from Afghan soil.
They also have had major manpower increases, which are even going on as we speak, through merging with splinters with Afghan Taliban officials playing a role in this. They had their high level leadership get set free when the Afghan Taliban opened the jails and let everyone out. Most notable of which was Maulvi Faqir who Pak tried to target in a surgical strike a couple months ago, shows how much of a HVT he was and he was let off scot free.
Then you got the glut of military arms which are all over Afghanistan, TTP has access to large caches of weapons as well as most importantly, optics, thermals and explosives etc...
So combine all of these things and you got your recipe for a resurgence which no fence alone is going to stop, only the combined layers of defense i.e intelligence, Military, Paramilitary, CTD, Police and so much more can help stymie the resurgence.
