My club has enough parachutes for every glider we have and it's pilot's choice as to whether to wear them. The vast majority do. Here in Canada the type certificates for German gliders are almost verbatim translations of the LBA/EASA documents and I've noticed that they all seem to have under "required equipment" a back type parachute or a cushion of dimensions approximately the same as a backpack chute (the FAA TCDS for the same gliders seems to omit this) so you've got a choice of a cushion or a chute. Odds of needing a chute are very low but if I ever found myself needing one and chose a cushion instead I would feel a bit foolish. I also think that in case of a crash or a forced landing in remote country the parachute canopy might come in useful on the ground.

The Slingsby Kestrel 19 TCDS here in Canada is odd - it simply flat out requires a parachute to be onboard during flight!