Reasons why I'm not in 90%+ probability of superintelligence short-term:
When we observe AI performing some task, it can be both an evidence in favor of AI progress and an evidence in favor of task being easy (see chess);
We are bad at noticing which tasks will end up hard (see Moravec's paradox and Dartmouth workshop) and we are bad at noticing existence of hard tasks, because we have poor introspective abilities about relevant parts of our cognition, otherwise we would be able either to introspect on it and write it down or at least to gather relevant data and train model in generalizable way.
Reason why I have 50%+ probability of superintelligence short-term:
Humanity has proven itself being better at designing compute-intense mechanisms like gradient descent than at careful study and design of intelligence, so it's more likely that next advance in AI will come from a new improved way to generate intelligence from compute and I expect AI swarms doing math research in learning theory to be really useful here.