Next L train at 8th Ave?

Why don’t they leave the doors closed on one side at 8th Ave and 14th St so you know which train is leaving next, like they do on the G at Court Square? This would be very helpful especially now that the “next train” sign is broken.

Why don’t they leave the doors closed on one side at 8th Ave and 14th St so you know which train is leaving next, like they do on the G at Court Square? This would be very helpful especially now that the “next train” sign is broken.