Oh wait -- they do! It's just a shame that most developers don't put anything really useful in there.:(
So even if you put a link there you need someone to be aware that such a link exists, to believe there might be something useful at the end of that link (which you point out, there rarely is), then wants to go to/turn on their computer, fire up iTunes, attempt to & succeed at finding your app, click the link, possibly register for your bug tracker (doesn't seem too uncommon), possibly check their email to confirm their registration and then finally file a bug report.
Anybody can feel free to contact me about this via my profile here, I'd truly be interested in making this flow easier and I know how to write this stuff.
Personally, a "report a problem" link would be a lot more inviting, especially if it let you send them a message from the app store, and include the last crash report (if it was the last one).
There have been a few times where I was lucky enough to be able to track someone down based on their username and personally contact them to help them out, but if they'd gone though official channels for support instead of via a review, it would have been much better for both of us.
I actually would like to see the ability for developers to publicly respond to reviews. Sure, some may abuse it by submitting nasty responses to bad reviews, but good developers would provide useful/polite responses, and that would be another signal users could use to determine if they want to buy the app in the first place.
Easy fix then: a small checkbox on review page "this is a technical problem", which will forward review and contact details for the reviewer to an arbitrary developer bugsystem.
I've never actually had one back which I think I take as a good sign, I don't think I've had a crash report on iTunes Connect either so touch wood it is pretty solid although I'm adding more under the covers error logging at the moment using Parse which makes it pretty easy (saved me a day or so setting up and securing a server to my satisfaction). This will mean I can log from later in a crash (if it happens) than I could from email as I don't need to pop up any views just send it although where possible I will pop up the email option.
