Because the Left is near-orgasmic at the prospect of taking any GOP state-wide seat from Texas. Trump won TX by 9%. Cruz is still polling at +4%, but was +9% earlier this year.
In Texas, with about 9m votes in 2016, that 5% swing is about 450,000 votes.
Anything that gives the Dems possible national traction in a solid Right-wing state should be opposed.
Remember Wendy Davis was supposedly within a hairs breath of beating Greg Abbot!!!