[jnwatson]

For the same reason why it took a long time for crypto mining accelerators to actually ship. It is more profitable to keep them for yourself.

[latchkey]

This is a popular myth. Bitcoin asic's were 'shipping' in 2012/2013.

Some companies definitely played games and mined with the asic's themselves (and then shipped those used asic's)... but in general, it was always a lot more profitable to sell the shovels than it was to mine the gold.