The entire goal of these API changes is to intentionally price third-party app developers out of the market without imposing a strict blanket-policy ban.
And the goal of this is to attempt to further monetize the platform on the backs of other people's content by forcing them to see as many ads and upsell opportunities as possible.
And the goal of this is to appear more appealing to current and future investors in order to drive up the IPO price and build demand.
And the goal of this is to make those with significant equity stake filthy rich.
The issue is that the changes they're trying to make are inherently hostile to the community whose free content and moderation has made the platform what it is today. And if the community decides to leave the platform and not come back, then regardless of potential for extra ad revenue, the inherent value of the platform will disappear because ads will be shown to less and less users. This is assuming people leave and actually don't come back, which remains to be seen.
The whole "front page of the internet" idea was pretty neat, and is a stark contrast to the days where each internet community had their own niche forum somewhere. Maybe we'll see some other platform overtake Reddit as the new front page of the internet, or maybe an old platform like Digg will make a resurgence. But that's a tall ask when Reddit is now so entrenched in that space.
Edit: technology -> platform, in the last paragraph above.