It's the default OpensStreetMap style, which was never intended as a cartographic basemap for visualizations. Its purpose is to facilitate editing of the underlying data... but it's also one of the "free" options out there and integrated into most map library examples. ("free" because it's community-supported and heavy usage is discouraged, https://operations.osmfoundation.org/policies/tiles/)
That's fair! While understandably it isn't probably a top priority, I'd highly encourage checking out https://docs.protomaps.com/pmtiles/maplibre . It can be nearly free to directly hit a single planet pmtile file, especially with cdn in front, and slightly more to put up a server in front of it (imo, not needed).
Anyway, awesome site regardless, and OSM tiles are fine if not abusing their hosting (this isn't I'm sure).
