Ask Trump. Third time I said this, Trump pull the deal out by himself, it was neither needed or wanted. I don't know why he did that but I can guess, because he is losing in the poll and the only thing he say he will do but didn't is to pull troop off Afghanistan,
Trump leave when we are in the middle of Resolute Support, Taliban activities were minimum during 2017, 2018, and 2019, so much so Trump's own National Security Advisor deem it is safe enough to transfer sensitive Military Article to Afghanistan, that's where the Blackhawk, Little Bird were signed to Afghanistan, and even deals with Boeing to sell Chinook to the Afghan.
Either the Trump's NSA team were shit, or got paid to do that, or it's really that safe to do so, the spike only come after Doha Agreement and after the Troop draw down. That's lead to increase Taliban Activities, not the other way around.
As for whether or not Taliban is capable fighting, name me one FOB, COB that was overrun by Taliban. I am not even asking you to name regional command base or big base like KAF or Bastion. Small FOB and COB only, name me some of them being overrun by Taliban?
There is virtually no way for them to take Bakhmut, they had tried that since July when they took Lysychansk, even if they somehow manage to take it, that would be moot because once Ukrainian took Svatove and Sieverodonetsk, and they will because the Russia is abandoning the line there, they can just isolate and encircle Bakhmut had they lost them, making that push pointless.