Sunlight turns them to stone. They cannot come up.

UVA (315–400 nm): no measurable effect at sixty minutes. UVB (280–315 nm): integument discolours at four minutes, rigidifies at twelve — the same calcification seen in isolated YMA-001. Skin without integument does not respond to UVB in the test window. UVC (200–280 nm), which does not reach a living surface under an ozone column, hits everything: integument calcifies in forty seconds; unprotected dermis begins collagen-equivalent cross-linking at ninety seconds and proceeds toward a mineralised, brittle mass.

The petrification myth is a photochemical mineralisation of a UV-intolerant organism and its grown covering. They do not avoid the sun because they are modest. They avoid it because their materials science was specified for a world without a sky.