According to my calculation we have about $35,000 in itemized deductions in 2018. TurboTax wants us to take the standard deduction of $25,300. Why is that?

You have to look at your allowable deductions.  For example, you can only deduct medical expenses that exceed 7.5% of your AGI.  And under the new tax law your deduction for state and local taxes is limited to a total of $10,000.

The $10,000 limit includes Property taxes as well.
And Charitable is limited to a percent of your income.

Our deductions are as follows:

Property taxes - $7,900
Medical expenses - $11,600
Donations - $9,100
Local sales taxes (Texas) - $1,700

AGI is $150,000.

7.5% of $150,000 is $11,250 so medical of $11,600 leaves $350 as a deduction.   Adding your other deductions is $11,150 total itemized - far short of the standard deduction.