Why were stone handaxes made in the same way for a million years?

Early man made some useful hand tools
And no-one could say they were fools
But the axes they made
They failed to upgrade
‘cause no-one could teach them the rules.

In considering the evolution of human intelligence there is uncertainty about when an effective language first emerged and there is also a mystery of the early stone hand axes, which were made to the same design for about a million years. If the early hominins who made these tools were really that intelligent one might expect that someone in more than 70,000 generations would have found a way of making better stone hand axes.

Almost certainly there were many occasions over those million years when individuals made potentially exciting and advanced tools but a new tool is only successful if other people know how to use it and reproduce it, generation after generation. And there must have been many tools which were made of perishable materials which are not recorded in the fossil records. For instance the earliest spears may have been made by sharpening wooden spears more than 2 million years (Did early hominins - like Lucy - use spears) and spears made some 300,000 years ago - are very advanced (Oldest wooden spear, Skilled hunters 300,000 years ago)

This suggests that a new tool will be successful - and if information on how to make a tool is passed on by simply watching and copying the process is likely to be much more efficient if the teacher can use language to explain the process and also to explain where the pupil is going wrong. This difference is likely more significant the more steps there are in the tool making process.

While there is not firm evidence (language does not leave direct evidence in the record until writing was invented) it seems likely that humans started making more sophisticated hand axes, and other flint tools, once language had reached the stage where it had become a powerful tool for reaching tool making.

[This is particularly relevant to my research on the evolution of human intelligence, My model suggests that there is a mountain to climb as tasks involve more and more rules - until the crest in reached - when, once a suitable language tool is invented - and from that point on ]the more you know the easier it is to know even more ...]