In youth sports, most of the times parents pretty much have to be the coaches. I define "daddy" ball as a derogatory term for when a parent coach gives preferential treatment to their child ... i.e., their child plays more often, bats higher in the order, or plays a position than they would otherwise merit based on their abilities. My opinion is that in travel softball this occurs about on about half of the teams that have parent coaches. With that being said, on probably half of the teams where it does occur, it's not that grievous that it really hurts the team or significantly affects the other players. Then there a few parent-coached teams where the parent actually treats his or her child worse than the other players, in some cases perhaps because they don't want to be accused of being a daddy-ball coach or put their child in a position where they are being accused of getting preferential treatment. Unfortunately, coaches' kids are sometimes under the microscope and parents of other players sometimes use this as an excuse as to why their child isn't playing as much ... similar to teams where there's not a parent coach and they complain about "politics".
Of course, there's pretty much no parent coach who thinks they're actually doing daddy-ball. Most are just like the non-coaching parents who think their kids are better than they really are. There are also a few who think that their kids should get preferential treatment because they are putting in all the time to coach. My ex and I had more than one fight about that while we were married (and a few other fights about her statistics which I won't elaborate on here!). I've also heard of players who told their parents that they would quit if their parent didn't play them where they wanted. But I will say that I also have seen some pretty horrendous situations where the parent coach just had no perspective about their child or just didn't care. I think that's the exception vs. the rule, but it definitely does happen and when you're seeking out a new team for your DD, that is definitely something to research. But for the most part, I think parent coaches do a pretty good job and the term "daddy ball" should not be used.
I actually don't think it's increasing in travel softball ... and I will give TSZ/OFC some of the credit for raising visibility around it, and helping keeping it in check. And of course most of us non-parent coaches started out as parent coaches anyhow!