Often because the page cannot use the back/forward cache. An unload event handler is the most common reason. Remove it and going back can feel instant.
The most important way to make pages eligible for the back/forward cache is to never use the unload event. Cache-Control: no-store can also block it and should be used only where needed.
Search your theme and app scripts for unload listeners. Swap them for pagehide. Then test going from product to cart and back on a phone.
Source: web.dev, Back/forward cache. Reviewed Sep 23, 2026.