It does take months, but during peacetime modern militaries burn a lot of money on "being ready" for a quick response when it's needed. Russia spent their "Ready to get dropped out an airplane whenever" guys at the start of the war, they failed to do anything noteworthy, now they have nobody with the training and resources to be able to do that. Not to mention Ukraine is now a lot more ready to blow a transport plane out of the air if they -did- want to drop over Kyiv.