Well the service will certainly gain more content over time... it's just in it's infancy, and unlike Disney+, it didn't have decades of back catalog content to supplement it's new content. In other words, if you strip out all of the old stuff from these services and only count the shows that were made in the last two years, you will find that all of them are pretty scarce on content.
Now for those with deep back catalogs... well, that may not be a plus to someone who isn't interested in watching old stuff. You can fill a room with DVDs, but if you are only inclined to watch each once, you end up with a room full of DVDs that you will never watch. Netflix and the like have a lot of stuff that no one will likely ever watch. Someone will, but the preponderance won't.
Then you have the old revolving door of content that goes on... studio A makes show A, airs it to death on their service, then farms it out to another service. So even a show you enjoy watching again and again isn't always going to be available on a service forever. They rotate in and out and about. So while you may think plunking down $14 for a month of HBOMax to see show X, give it some time and that baby will eventually end up on another service down the road... and likely for much less.
Reminds me of Stargate SG-1 which was a Showtime original. Now you can pretty much watch it everywhere. It's still "new" content to someone, but for those who watched it originally on Showtime, it's now an old show to them.
