What I mean by a "spectator sport" in this context is primarily that the event can be monetized because huge numbers of people will watch it either in person or via video of some sort.

The number of people watching the trans-europe or other similar solo events as they happen is likely less than the population of a typical US liberal arts school. The monetization that might follow from YT videos that occurs later is completely different from what the TdF manages to encourage. The winner of 2023's Tour Divide has 58k views ... even Lael only gets 300k or so views for her adventuring and racing videos. This is not a spectator sport in any sort of historical sense of that term.