App Lab is not same as Sidequest, user not require developer account and setup a pc to install, just find the app from web browser then purchase it directly from Oculus or add it to Wishlist and then it appear in the user Wishlist in Quest store.
There are many website listed all app lab apps, the developer have to worry is the rating of his app, not app lab popularity. All the VR website and youtuber will introduce app lab to user, later everyone will know app lab is like pre-release app and a lot of good apps in there, just find them from website that listed them.
For indie developers with 1-5 people, earning 1 million is good enough and it will continue selling more and more as more VR users is coming every months, if the app is popular it earn 1 million every year. Compare to small studio with 15-25 people their yearly cost(total salary) is 1-2 millions, their app price have to be $15-25 to cover the cost.
Why the app does not sold much is because of the price. If the price $2 or $5 user will give it a try and give rating of worth buying it, this bring the app popular, but if the price $10 and above, user would want to save the money to buy other apps that they are more interested like Beat Saber or Saints & Sinners.
Pavlov is free in app lab, are the developer missing a lot of opportunity to made money, no, it is marketing, more users in the game more popular the game become and there are much more users coming to VR, more than existing users, they earn big from there.