B+ Trees don't have data associated with interior nodes. More keys can fit on a page of a memory. Therefore, it will require fewer cache misses in order to access data that is on a leaf node.
Data in B+ Tree is stored in a way to make optimum use of locality of reference. And We know that Disk access time (ms) is much higher than memory Access time (ns), So, it takes more time to access a page from Disk, so We want to retrieve as much as data in one go. So, we use B+ Tree instead of BST.