From Bearing Arms:

That’s why the NRA said that it ought to be regulated – NOT banned.
Why? Because politicians [had the votes] and were building steam [in 2018 Congress] and moving toward a ban on all semi-automatic firearms. Frankly, I find it curious that the Obama administration approved the sale of bump stocks, to begin with – but that’s another debate for another day. [the call for regulation by the NRA took the wind out of this legislative effort and moved the bump stock ban, now a “rule” instead of a law, into the regulatory realm where it can now be argued against (lawsuits have been filed ) and ruled on by the courts.]