Why would they? the X memory setup was a far bigger change and didnt bring any issues.
If the game is highly optimised for the original hardware,
and if the change to HBM doesn't bring any great improvement in bandwidth, they
might end up breaking the original optimisation - leading to frame rate drops etc ..
One possible example I can think of is if the original software is optimised to fetch data in the exact size (and aligned to) the original GDDR6 data width .. the changed to the wider HBM data bus width might result in much reduced utilizations of the wider bus - could even be a disaster for performance .. but I need to think about it more.
Working extreme example - original game uses scattered 32 bit wide aligned data fetches .. when shifting to 128 bit data bus width (HBM) those 32 bit fetches now are ultilising only 25% of the available bandwith.
It's an extreme example.. maybe/maybe not [the old adage -
if it can break it will]