I'm sure they want to use denuvo as well, but there are a couple "big" problems with it. First of all most of vns are 32bit while Denuvo only supports 64bit, which means they have to change to 64 as well. Then there is the "cost" problem, Yeah denuvo is currently uncrackable and most of AAA games use it, but they are selling millions per game, so they definitely don't care about its cost. But eroge sales are going rapidly down, seems like currently an average eroge sells only 3000-4000 copies according to Akabesoft manager, which makes it very hard to afford. I'm sure everyone can see the difference between those.
Also the DRM they used wasnt "shoddy", its a pretty hard to crack one, normally it'd take at least one or two months until it get cracked (Hell actually I dont think any visual novel crackers would be able to crack it). The problem isn't DRM, its the "Trials". As long as they release trials their game will get cracked no matter what they use, even denuvo. There are only two ways of this; They have to make some completely new engine instead of using KiriKiri or They have to stop releasing Trials.
+ This is not the end of the problems; Denuvo is not a DRM, its a security system which "protects" DRM. This is the reason why he wants to release their games at steam; without a good DRM there is no point of denuvo, and the "Buddy" one which everyone uses is certainly not that strong. So you'll have to pay for a DRM as well even if you somehow can solve all those problems. In short the road of the uncrackable visual novels are hard as fuck, it is not impossible but doesn't seem like will happen anytime soon either. The key point is "Kirikiri", if they can somehow upgrade it well enough or make some new strong engine system for themselves they can make this happen, but most likely it'll take a very long time and denuvo will be cracked by then.