Because two dimensional geometry is a subject most used to think was totally worked out, until a while back with new results like the Penrose tiling.
Most theorems in maths are rather recondite and many are in new fields also. It's fascinating to have new results in a field that has been studied so thoroughly for so long.
If you could prove something like Pythagoras theorem for the very first time today - or prove the classification into 17 wallpaper patterns for the first time - it would be equally interesting, but it is too late for that - those results were proved long ago.