Alexa rank for wikipedia is 13, OSM is 4550. It's not on the same planet. No, not on the same galaxy.
Wikipedia is not only read and written by the entire planet of humans, including the smallest 3rd world countries, it's also a bot feast, and busy powering APIs all over the world.
It got hundreds of links in some articles, which are automatically connected to all other articles in a gigantic graph of data. Oh, each article may also exist in a hundred languages, times each version, thanks to the history of all edits ever performed or suggested.
It's not just links though, now articles have plenty of metadata that generate connections, tables, ranks, toc, indexes, hierarchies, and listings as well.
All that is edited, rollbacked, debated, diffed and rendered almost on the fly for millions of articles, while respecting the permission system, and of course, the fun part, detecting the thousands of attempt at abuses by second.
In the blink of an eye. Because wikipedia is _fast_. It's one of the fastest site around.
Of course now it is also serving billions of images, sounds and videos. And the foundation is also maintaing:
MediaWiki
Meta-Wiki
Wikibooks
Wikidata
Wikinews
Wikiquote
Wikisource
Wikispecies
Wikiversity
Wikivoyage
Wiktionary
Not to mention animating workshops all around the globes, helping NGO to provide offline wikipedias for poor countries and providing and maintaining the wiki as FOSS.