Why aren't there HiRISE observation footprints near the Martian poles?

HiRise routinely observes at high latitudes. In fact I can quickly find these examples:

• At $86.8^circ$: https://hirise.lpl.arizona.edu/ESP_035295_2670
• At $82.2^circ$: https://www.uahirise.org/ESP_027324_2625
• At $87.9^circ$: https://www.uahirise.org/PSP_010623_2680
• At $85.8^circ$: https://www.uahirise.org/PSP_010636_2660

You have a large gallery of high latitude examples here: https://www.uahirise.org/science_themes/polar/index.php?page=159

So, the problem is not that MRO avoids the region but seems to be related to the online HiWish Browser Map app. My guess is that the projection makes huge distortions on the image footprints and thus the software doesn't renders them (due to the code needing some enhancements to allow it or due to a conscious decision to avoid confusing visualizations of the rest of the footprints at high latitudes).

In the help section of the app you can read

Near the poles, the elevation map will be better registered than the visible (and polar IR is not yet available through this interface).