There is nothing stopping the OSM Foundation from say, offering a complete SQLite (or PMTiles) tileset download on planet.openstreetmap.org, technically, legally or otherwise. Creating and archiving the tiles shown on osm.org would be at least a couple terabytes once you get to around zoom level 16.

The key distinction is "official" - the only "official" data product of OpenStreetMap are its XML and PBF data dumps at planet.openstreetmap.org. The frequently-updated tiles you see on osm.org are "quasi-official", they're created by a separate project called OpenStreetMap Carto. These tiles have a special status within the OSM ecosystem for historical reasons; by virtue of OSM being map data, it should probably show something for human eyeballs on the website.

The design goals of OSM Carto are to show feedback to map editors; the linked vector tiles project is intended as a successor, or at least complement, to OSM Carto. The consumption of the tiles by third-party sites is a side-effect tolerated by OSMF; the general consensus within OSM seems to be that a consumable tile service for third parties is outside the scope of the project.