It’s not just Democrats in open primaries, it’s Independents. Two in my family have gone Independent because they’re sick of Republicans. That’s actually Trump’s base. Many like me have stuck with Republicans to have a say but many Republicans don’t recognize the danger and think it’s business as usual.
Thus, Cruz.
It is nice to be independent But the closed Republican primaries do not allow independents to vote. That is just fine with the GOPe as the more establishment Republicans can thwart the will of the larger conservative electorate.