Sports car endurance races are far too long, and far too physically/mentally demanding, for one driver to complete safely. Most WEC and IMSA races run anywhere from 100 minutes up to 24 hours, and the format is built entirely around teams sharing driving duties. 

Balance of Performance (BoP) is a system used in multi-manufacturer racing classes – most notably GT3-based classes like LMGT3, GTD, and GTD PRO, as well as WEC's Hypercar class – to artificially equalize performance between fundamentally different cars, so that a wide variety of manufacturers can race competitively against each...

The FIA World Endurance Championship currently races just two full-championship classes, though a third class appears at Le Mans specifically. 

Sports car driver grading is the FIA's system for classifying every driver into one of four tiers – Platinum, Gold, Silver, or Bronze – which then dictates who can legally be paired together in a car for Pro-Am classes like LMGT3 and GTD. 

The IMSA WeatherTech SportsCar Championship currently runs four classes on track at once, split between two fundamentally different car types: purpose-built Prototypes and production-based GT cars.