Because the SENTINEL1 images are only every 12 days in the eastern part of ARGENTINA
Can you request that this change?
Is there a cost?

The acqusition scenario is managed by European Space Agency, you can find more details here:

You need to contact them for the change, but I honestly doubt you will be able to achieve something.
Sentinel-1 is following a “monitoring observation scenario”, not a “tasking” one, so individual requests are rarely taken into account (only in the case of natural disasters, etc.)