A number of issues stop that from being possible.

First, a flare is meant to be an emergency system. You send material to the flare because something has gone wrong, like a fire or a leak. There needs to be a clear path from the plant to the flare to make it as easy as possible to remove the material from the plant, so putting a turbine in the path could impede that.

Second, flares are typically used intermittently. Optimally, they would never need to be used at all, but the reality is they will be used. So that turbine would be sitting there on standby, producing nothing most of the time. And then it would suddenly be producing a lot, to the point where there could be too much gas for it to handle and the turbine would have to be shut down.

Third is cost. Gas turbines are expensive to maintain, and a gas turbine that’s sitting there giving you nothing most of the time is even more expensive cost/benefit wise.

That would mean investment and corps won’t do that. They want all investment to be done by the gov’t, ie: our tax dollars instead.