They're not really enterprise apps. They're just betting odds displays. But I hear you on the criticism of enterprise software still. I just don't think it's the thing here.
Why would betting odds displays escape from Enterprise Java? Seems like the kind of thing that would get it in spades for regulatory and CYA reasons.
They could still be enterprise apps. From what I've seen of them, they appear to be little more than what you'd get off espn if espn were 100% betting. My point is it's not the system that they use to sync up lines and whatever...I think.
Usually culprits are things like downloading multiple data files in a single threaded block, or insanely deep object graphs with thousands of memory fetches per real operation.
That's not really anything to do with the technique (code in browsers) or the runtime (JVM) or even the programming language (Java) -- and everything to do with poor development.