Why does Gaius Plinus the Younger not accompany his uncle on the expedition to Pompei

Gaius Plinius the Younger, also known as Pliny the Younger, did not accompany his uncle, Pliny the Elder, on the expedition to Pompeii because he was unwell at the time. Pliny the Elder led a rescue mission to the area affected by the eruption of Mount Vesuvius in 79 AD, while Pliny the Younger stayed behind due to his poor health.