That's literally the last thing a rational Taliban decision maker would want to do.
20 years after getting kicked out the Taliban are back in power. They did just fine oppressing Afghans from 1994 to 2001, even as the international community condemned their behavior.
In August 2001, if anyone had told me the US would invade Afghanistan and end Taliban rule, I'd had have a good laugh. While the world knew of the Afghans' suffering, these were far and distant events and the Soviets had shown how much of a hornets nest the place could be.
The only reason they got invaded? Their careless involvement with Bin Laden and - indirect - killing of many Westerners.
20 years later later the West has tired of that war. The last thing the Taliban want to do is to provide Western electorates a reason to send soldiers in again. Killing of Western soldiers or Western civilians could, potentially, galvanize Western opinion against them again.
So could, but less likely, credible reports of Taliban massacres of Afghans. That's why their PR people have been at pain to say that there will be no revenge or retributions. Reports are starting to surface that this is only pretend talk and that in fact the Taliban are not very different from before. But that is plausibly deniable and will be kept that way. Overpowering the airport or evacuation procedures would negate any such claims.
Once the immediate rounds of evacuations have proceeded and the airport has, voluntarily, been evacuated by Western troops, things will be much safer for the Taliban and there will be no easy "beachhead" into a country that is, largely, only accessible by air. In short, they will be back to pre-2001 days, but with an extra dose of "never get involved in a land war in Afghanistan" thrown in.
How they will proceed then is indeterminate - the diplomatic situation wrt China and Russia is much more favorable than it was in 2001 and there was another question here about diplomatic overtures. They may want to be moderate and gain partial Western acceptance. Or they may want to stick to their ways but rely mostly on non-Western support. They probably will steer clear of direct involvement with Al Qaeda-type international terrorism. That's all speculation on the future.
But not "conquering" the airport right now is mostly common sense with regards to avoiding further Western interference.