What it all really comes down to is money. Generally speaking, good effects work, be it practical or digital is always more expensive than bad effects work. When it comes to blood effects, even good practical effects are I imagine a fair bit cheaper than even bad CGI. As I said before, the reason why CG blood is used at all (aside from poor judgement and laziness) usually has to do with how much control the director wants over the shots and how much time they're willing/able to spend on a given scene. Again, like I said before, once you start letting off blood squibs, you're going to end up with a set full of actors and costumes covered in the stuff and if something went wrong, or the director wants another go at it then it could take *hours* to reset everything for a second take and every time this happens it's burning money with little footage to show for it. Alien and the Thing each had a very elaborate and gory practical effects shot that didn't go off as planned and sure enough, it took forever to reset. Luckily I think they both got it on the second take but crews aren't always so lucky.
With CGI blood you have total control and can just focus on the actors and the performance. Of course if you're David Fincher this works great because you have a respectable effects budget and a habit of doing LOTS of takes, plus it's just one or two shots. For a mid-to-low budget horror or action director it's not so good because (hypothetically) you have a whole movie full of hacky slashy or car chases and giant fireballs and you can only afford some D-grade effects house to quickly do all the bullet hits. Squibs might have looked better, sure, but the money saved on NOT doing multiple resets on every angle of the gore scenes made it a good business decision, if not a good creative one.
Bottom line, as I've often said to people who complain about CG; there's nothing inherently wrong with it, it's just another tool. Like any tool though, it can be misused or used as a crutch. When it's used properly you won't even know it was used at all (again, check out Zodiac.)
