Welcome to the forum, Emile.
Why? Because everything in software development takes time, Dorico has a small development team, and this particular thing hasn’t yet reached the top of the priority list.
It has been stated in the past couple of hours that a new version of Dorico isn’t expected in the next 30 days, so I think I can say relatively safely that you are going to be waiting months (or perhaps years) for an official solution. Every program has its strengths and weaknesses, and while playback of ornaments is currently one of Dorico’s weaknesses it’s quite likely that if you go elsewhere you’ll find other weaknesses that are Dorico’s strengths: great engraving out of the box, perhaps, or intelligent note grouping, perhaps, or an interface that looks and reacts like as though it was conceived this century, perhaps
If you’re really desperate you could add a stave to a player, if it’s a solo player, or add a divisi to your player, if it’s a section player, then manually write out the ornament in that extra stave (or division), then delete the stave again. You should find that Dorico still plays back that music even though it’s not shown on the page.