A lot of people (scientist included) blindly apply the direct analogue of feature and environment.

On Earth, as you observe, most (but not all) of the polygonal features are due to freeze-thaw action during ephemeral warm episodes.

Using this analogue, a lot of people who should know better point to Mars and say "polygons-freeze/thaw, therefore Mars must have been warmer in the past"

In fact, polygons can also be formed on Earth by solid-state (fully frozen) expansion and contraction - either as thermal shock, or as slow and steady contraction - basically cooling cracks.

IMHO, all, or almost all, of the polygons on Mars are formed in a similar way, so we don't need to invoke a different Mars than we see now.

However, I admit this an area where work is still ongoing and we need to wait and learn more.