Bing because it's the default on their web browsers they've used in college and work.
But moreso - whatever the default is what they use. They have zero attachment to Google.
Bing shows no signs of marketshare growth: https://gs.statcounter.com/search-engine-market-share
I noticed that website doesn't show the absolute numbers involved in search engine use.
And you ignored the part where I said "they use the default".