I'd speculate it's been a combination of two main reasons:
1) They haven't felt it would be profitable, and couldn't afford to lose huge amounts of money in finding out.
The market for TSS has been mainly a relatively small number of turkey hunters. Keep in mind the majority of turkey hunters are making their purchase decisions mainly on price, still opting for lead turkey loads, not even opting for the HTL (simply "heavier than lead") superior turkey shells which are widely available and less costly than if they were loaded with TSS.
2) Increased liabilities. There is less liability when a handloader purposefully chooses TSS for his loads, since the liability I'm talking about is the increased range of it being lethal, and how much more it will penetrate compared to lead.
But with more awareness being raised
would be nice to see Federal come out with a new "Super Heavyweight", maybe with an initial offering in #8.5 size shot.
Federal has already "pushed this envelope" farther than any other major manufacturer (with their "Heavyweight" line).
Winchester has gone the opposite direction, trying to market longer-range lead shells, and currently doesn't even manufacture an HTL turkey shell. Neither does Remington. At one time, I was very pleased with the Winchester Extended Range HTL turkey loads, which I liked much better than other brands.