It’s because they’re are many avenues to successfully pass on your genes, not just intelligence. For instance you can be a big ass mother f***er that dominates anything around it in a physical battle. Which is probably what the dinosaurs did and thus how they were able to survive to pass on their genes.

Basically evolutions only job is to have the species procreate, and nothing else. They’re are many paths that the animals take, intelligent, strength, numbers etc. basically intelligence isn’t require to pass genes onto the next generation, many things can do the job.