Because it's all abstracted away. B-trees are used in the underlying implementations of RDBMS. Other data stores such as MongoDB, Memcached, and Redis use has

Because it's all abstracted away. B-trees are used in the underlying implementations of RDBMS. Other data stores such as MongoDB, Memcached, and Redis use hash tables. Arrays, linked lists, and dictionaries are usually abstracted away by whatever scripting language is in use. I can't think of common use cases for data structures like heaps/priority queues and graphs. Both come in handy for dependency management and loading assets from disk, like in the case of writing a package manager or a game. But nothing that complex is needed for your typical web app.