Let's offroad / mountain bike / mtb / ride dirt

A higher grade stainless spring should/could be lighter than a Ti one

Well that was certainly how Fox tried to market the SLS springs but in reality they were never actually any lighter that any of the old school Ti springs from the mid early 2000's.
The weights were similar on lighter springs around 300lbs but if you needed much over 450lbs they certainly are not lighter than proper Ti springs. But it was still a fair weight saving over a standard steel spring.

Super Alloy Racing springs came on the scene with springs that were arguably lighter than normal steel springs. But they used springs that were a fair bit shorter in overall length and then used plastic spacers at either end to fit them on to a wider range of shocks.

SAR springs are produced by Eibach in Germany and its worth noting that EXT springs are also produced by Eibach. Early EXT shocks were occasionally seen with coils that were marked with a white Eibach logos before they started marking them as EXT.
My 140mm long 550lbs EXT weighs 447g. Better than the roughly 750g of a normal steel spring.
An old school Ti Spring at 550lbs would have been around 350g depending on brand.
I have shorter EXT springs that measure 117mm and rated 450lbs, they aren't easily accessible right now but I'll weigh them later.

I guess no one bothers to produce Ti springs due to the cost and that current light weight steel springs are close enough.
Theres also the fact that the quality and ride feel of air shocks massively increased over the past 10 or so years.
Coil shocks are definitely still a bit niche but they do seem to be making a bit of a come back over the past couple years. Most of the folk who switched back to coil from air like me tend to be of a certain age who never gave up saying "air shocks are shit! coil more plush!"