Greeting Pilots not allowed?

I've flown with Qatar about four times over the course of the past two months. After every flight, when most of the passengers have already disembarked I politely ask the cabin crew if I can meet the captains.

And I'm always met with an almost condescending refusal.

I understand the crew may be stressed and overworked but is it strictly not allowed?

I'd love to hear about anyone's experience on this