I'm surprised by this because Netflix has Heartstopper & Neil Gaiman's Sandman. They've also canceled a bunch of stuff that could come back really strong, Sense8 comes to mind.
Sure, yes, but Heartstopper was a risk and Sandman, one of the more bankable IPs, was kept in limbo for a new season until the last few weeks for fear that not many people would want to watch it (probably an indicator in and of itself as to why all their original shows were cancelled)
Realistically the second season of Sandman and final season of Stranger Things probably won't materialize until 2024 given how long they take to produce.
I recall reading that Netflix intentionally capped the production of successful shows to avoid overpaying for actors. Actor contracts apparently have predetermined rates for 3-4 seasons, and then must be renegotiated. For a successful show the actors can have immense leverage (see Seinfeld).
Netflix thought they we being smart by doing this, but they may have simply upped their content risk and simultaneously convinced top talent to work with other streamers.