The event is already massively popular and only going to get more insanely popular as time goes on. Making more people come to the event is literally one of Universal's top priorities every year. Longer lines are something people should love to see. More popular event means bigger, better events in the future. This isn't a local cult haunt, it's a world renowned Halloween attraction and Universal wants to present it as such to as many people as humanly possible.
Also, the second bit about 'teenagers and young people' is exactly why I would have loved to see an Eilish house. The house and event in total could help birth future fans of the genre in a big way. Maybe there's young people who would go to see Eilish, end up going through the Beetlejuice house (when they have no idea what that property is outside of 'spooky' Tim Burton imagery at Hot Topic) and they love it so much they end up watching the movie and enjoying that too.
Finally, I could just as easily say the group that's actually annoying and disrespectful at HHN in large groups would be adults who like to drink too much and 'tough talk' their way through houses but that would be demeaning a large portion of the audience just because I've personally seen some dumb people acting dumb before. Stupidity exists in all forms of person so let's not try to look down on one portion of the crowd just because they're a different age group than us.
There's always a sentiment of 'we're the actual hardcore fans of HHN so we should get the most enjoyment out of the event, obviously' that somewhat permeates this board and it sometimes needs to be checked a little. I get that it's part of the territory when you love and are passionate about anything but we have to remember that this event is open to everyone in the world (age appropriateness aside) and that is actually a good thing, believe it or not. Whether you've been attending the event 19 years running and can operate as a paycheck free tour guide through an anniversary haunt or this is the first year you'll be going because you love Billie Eilish or you grew up watching Beetlejuice every third Sunday when your grandma babysat you, the event will be just as fun for everyone.