I'm an over 65 widow. My spouse died in 2018. Why is my standard deduction for 2019 $13,850? Shouldn't it be $24,000?

No, it should not be $24K for 2019. Back in 2018 you got $12K for you and $12K for your spouse even though they passed that same 2018 tax year.

In 2019 it's just you and only you. So you get "only" the $12.3K standard deduction for you only. Since you're over 65 you get an additional $1,550 for a total of $13,850. That's it.

sorry for your loss....

the $13850 is correct.

for the year of death, it's still a joint tax return, so the $24,000 was used. that was correct 

but beginning in 2019, you are filing single, and since you are over 65, the standard deduction is $13,850. 

You could file as a 'qualifying widower' for two years (2019 and 2020) and get the $25,400 standard deduction if you had dependent children that lived with you....  but otherwise, it's the $13,850.