‘We are witnessing a moment where growing numbers of women and girls see death as preferable to living under the current circumstances,’ a UN official has been quoted as saying
They are being blocked at the border. The Taliban won't let them leave. The ones who got out and participated in interviews (ie the ones we hear about) talk about how their families back home are being harassed, hiding.
Getting caught trying means lengthy torture, ending either in death or crippling injuries.
And, because women's movements and activities are already horribly controlled, even attempting to run is almost impossible. Getting caught is pretty much guaranteed before they get anywhere near a border.