Because if you are a microchip manufacturer in the 70s:

• Calculators are a reasonably good revenue stream once you’ve developed a chip, but needs a ton of upfront investment
• Defence contractors have essentially unlimited budgets from DoD, need chips, and are more than willing to pay for all the R&D to get what they need

The entire US tech and aerospace industries are built on what is effectively massive government subsidies in the form of weapons contracts