Through MARPOL annex VI the IMO focuses on reducing the carbon emissions “globally”
This was the prime intention behind making ANNEX VI mandatory( as a part of Marpol)
The process was further accelerated by introducing a sulphur cap in 2020 which aims to further reduce the emissions at a global level and not local level.

The idea behind not including the annex vi in PWC is that IMO decides not only on the basis of environmental considerations but also the commercial viability

The other reason is the density of traffic in polar waters which is very less compared to the other parts of the planet which impacts the global warming issue predominantly.

The other reason is the availability of optimum resources in polar water reasons including the current designs of engines and machinery. I am sure member states wont let it happen soon

Having said that
IMO is still figuring out the possibility of cleaner fuels which impacts the environment globally than locally.

The decisions at IMO are also subjected to widely conducted scientific research.

The issue of ‘black smoke’ in polar waters is a bigger challenge than anything else currently
The work is under progress on that.