Why do the french use the accent circonflexe in the words foret ile hotel?

it is used as a reminder of a past "s" in the Word.

- "forêt" was formely spelt "forest"; the Word "forestier" (from the forest) kept his "s" and did not adopt the accent.

- "île" was spelt "isle";

- "hôtel" was spelt "hostel" or "hostellerie".

The same goes for "hôpital", formely spelt "hospital", which gave the Words "hospitalier - hospitalité - hospitaliser" and many Words including the circumflex.