original mario on nintendo switch - warp zone to 8?

It seems that the version of Super Mario Bros. you are playing isn't the beloved 1985 NES version, but a 1986 arcade version called VS. Super Mario Bros. Most likely because the NES version is only available through the paid Nintendo Switch Online service, while the aracade version is sold in the Nintendo eShop as Arcade Archives VS. SUPER MARIO BROS.

This version is different from the original one in many surprising ways. Some of the changes are there to prevent bugs, like the famous minus world bug. Other, like removing several 1-ups, are to make the game harder. Sometimes entire levels have changed places or are swapped for Lost Levels levels.

The difficulty tweaks includes changing the 4-2 warp zone to only include the warp to World 6. This way players are forced to play through worlds Worlds 6 and 7 which include some really devious levels from Lost Worlds.