Some cars have
There was 50's era MG that used them.
I couple of model years of Toyota MR2.
The E46 BMW M3.
Some reasons manufacturers that have used them and dropped them is user complaints.
It shifts hard.
The consumer isn't used to the idea of going down through all the gears just to get to 1st.
It's louder and sounds unnerving
In BMW's case consumers where allegedly bringing in their cars for warranty when nothing was wrong.
There are claims that they don't last as long as other transmission types although I am unable to validate that.
In car racing, they are very popular
Here's a website that builds them for various classes. GT1 and GT2 WEC are rife with constant mesh sequential transmissions.
Hollinger Racing builds them to swap out the stock transmissions of various homologated vehicles.
But to me, an SMG is music