This is probably because the Brewers as an org also can't really hit the splitter. 😯
I'm kidding (kind of. not really. maybe just a little bit. Or not at all). I mean RHP Tanner Shears has about one of the filthiest splitters I've seen in the past several years. One of my biggest heartbreaks heading into this season was I wasn't going to see the further development of that pitch.
Anywho, as to Holub, the splitter is a relatively new pitch for him with varying levels of control. In his last interview with Jeff Hem of the Sounds, he didn't even mention the pitch. It was all fastball and slider talk. I personally see the pitch as an off-season development akin to RHP Shane Smith developing the slider in the AFL last season. But, to your point: when he is throwing it it is pretty dang nasty. I could have sworn I've seen him use it in several outings of late with the Shuckers. But, I'm an old geezer who often makes wild n wooly claims on the basics. As you both know and love to point out 😆