I think a key reason they missed mobile is that it was during Intel's peak dominance and growth. Mobile was smaller, less powerful chips at lower prices and lower margins than Intel's flagship CPUs in that era. The founders who built the company were gone and Intel was a conglomerate run by people hired/promoted for managing existing product/category growth not discovering and homesteading new categories. They managed the conglomerate with a portfolio approach of assessing new opportunities on things Wall Street analysts focus on: margins, total revenue, projected market size and meta-metrics like 'return on capital'.

It's classic Christiansen "Innovator's Dilemma" disruption. Market leading incumbents run by business managers won't assess emerging unproven new opportunities as being worth serious sustained investment compared to the existing categories they're currently dominating.