i think the tax charge is also a big factor.
e.g. dubai tax is just like Aed30 while Doha is Qar480... if im not mistaken.

i got my ticket doha-dubai-manila-dubai-doha for dec, for about QAR2800, while ticket for doha-manila-doha is likely QAR5000... almost double the price.

direct flights are really expensive from doha.