By creating near-universal exclusive contracts with venues and artists.

Ticketmaster/LN offers venues ticketing access to fans who want to buy tickets. Because there's no real competitor, the venues feel compelled to sign. The contracts have a provision that prohibits the venue from contracting with other ticket sellers.

Ticketmaster/LN offers artists access to venues for a national tour. Because major venues have all contracted exclusively with Ticketmaster/LN, there is effectively no way to tour without participation of venues who exclusively use Ticketmaster/LN. It's a fait accompli at this point, but Ticketmaster/LN also offer artists participation in their bogus fees, meaning artists get some extra money and don't have to take the blame (Ticketmaster/LN takes the blame, and some extra profit). The artists' contracts prohibit working with non-Ticketmaster/LN venues, further locking in the venues.

Venues who do not participate are locked out of artists and fans. Sounds like a blacklist to me.