There are various reasons why sentients do not all ascend to higher intelligence (or as we call them toposophic) levels. Among these are
- Ascension means dying to one's old self, many people are attached to their current status.
- Ascensions sometimes go wrong.
- Ascension technology may be restricted in some polities.
- There may be ideological, religious, peer-group, or memetic pressure against it.
- Ascension requires great discipline, dedication and training (although there are 'godseeds' and similar devices that can greatly accelerate and ease the process, these can also have rather unpleasant side-effects if one is not psychologically balanced).
- First Singularity (S1) and higher intelligences are perceived (rightly or wrongly) as working hard, and human-equivalent beings may not wish to give up their life of pampered indulgence.
- Some worry about real or more often imagined negative events (loss of human feelings and appreciation, loss of sensual desires).
- Many are just unlucky enough that they'll never recognize an opportunity to ascend.
Beside all the obvious and less obvious reasons, most beings do not have a strong incentive to ascend. It is an awful lot of work that cannot be left to the AIs. Even ATMs, Automated Transcendence Machines, essentially force the ascending being to do a lot of re-evaluation and personal change, which makes most beings, habituated to live in comfort, less interested in ascending. Those who wanted to ascend did so long ago and left behind a culture of those less inclined. Over time the fraction of ascenders went down, and a steady state emerged.