After the impact of the MGM hack this year Cesars probably revisited their insurance on getting compromised. After the auditors and lawyers looked at all the risks they came across DEF CON and said no because of the wording of how DEF CON is marketed. Their choice was probably to drop them or loose coverage. DEF CON is listed as a "hacker convention held annually in Las Vegas, Nevada." where Blackhat is "Black Hat is…
It doesn't provide information, it just provides sales suits a chance to blow their hot air :P
If I'd ever go there it would just be an excuse to go to vegas to see DEF CON as well :P I work in security but I have no time for corporatism and sales bullshit.
Edit: I know it's a bit of a hot take but I've been to so many conferences where sales goons spew all the pretty pictures and then later when we actually got our hands on the product it turned out that it couldn't do half the stuff that was promised. Or there were other weaknesses like excruciatingly bad support. I've become very cynical due to this.