Previously, Epic Games took back Fortnites highly appreciated Shopping Carts which allowed players to not only travel faster but also get some pretty spectacular kills. This was due to the increase in the number of issues; players were coming across with the implementation of the so-called vehicles.
However, now the developers had had some time with the shopping carts, they have been re-enabled with the release of Fortnite newest v4.4.1 Update.
Source: N4G PC Fortnite Update v4.4.1: Shopping Carts Are Back