It's a really odd change. The merchant used to sell everything at all times right? I thought that was a smart way of giving players future recipes to wonder about and look forward to.

But with this, there's no signal or explanation that a change takes place. Theres no in-universe justification -- like is the flesh stuck inside Bonemass's body?

It's also removes what I had always thought was a well-designed sequence break. Frostner and the Sledge are fantastic for swamps, with one coming at the risky cost of sequemce breaking into mountains first - a risk worthy of reward. This change just removes one more meaningful path of player agency.