This isn't (just) a regulator issue: it's a market issue. There just aren't many new engines produced every year, because there isn't demand for it. Owning an airplane is expensive, even on the lowest GA end. It's a hobby for the affluent and wealthy. The market just isn't that big. On the extreme side--private jets for the ultra-wealthy--it may be different (I wouldn't know; I'm a lowly 7-figure net worther, barely "rich" by this standard, and owning a private multi-engine jet is well beyond my means).