I flew several times in the upper deck. The experience was great, a kind of cosy place in a huge plane. I wonder why all airlines do not put their 1st class th

I flew several times in the upper deck. The experience was great, a kind of cosy place in a huge plane. I wonder why all airlines do not put their 1st class there (Lufthansa for instance is business on the upper deck, while IIRC Thai is first)