I found nowadays developers tend to use gypsum plastering for indoor wall

A layer of thin cement plastering on brick then a layer of thin gypsum plastering on top cement again
Instead of a thick layer cement plastering on brick

Any benefit from using gypsum plastering?

Easy for developer. Faster, No shrinkage so no crack like cement if poorly done or wrong method.

You can google comparison in Internet

https://happho.com/gypsum-plaster-advantages-disadvantage/

And cheap tooo for them..

Is gives smoother finishing compare to just cement plastering.

so it is all about cost + time + work effort effective

yes, i do found that recently made houses (below 10 years) tend to have smooth finishing wall comparing to those old school unit.

from structure pov, i don't need to have a beam underneath to take a load, brickwall are heavy. less load mean reduction in beam and bar sizes which ultimately affects foundation works. this gypsum wall is light and allow to adjust room size without the need to redesign the whole structure. as gypsum wall is not a permanent structure, it can be used to skirt lighting, ventilation requirements of a room.

skim coat used for smooth wall finishing looks good, but for me, it is a cosmetic effect to mask poor plastering skills.

I think it is usually called skimcoat over here. There is base and finishing coat for it. It is still the same work sequences, just that the thickness of the wall may be reduced (More suitable for AAC block and internal wall).