In my experience (doing what ppl in this forum seem to call "sutta jhanas," as taught by Bhante Vimalaramsi), it is just as some of you have said -- if you WANT the jhana, you ain't gonna get it. So if you got there, it is because you have (temporarily) renounced some craving. This gets more and more subtle as you progress through the jhanas. Any tiny little "ah, let's make this happen" can throw you off balance and give you a restless sit. It can be super frustrating.
Especially when you have a great sit one day, and -- even seemingly subconsciously -- think "oh cool, now I can do that, let's do that again tomorrow!".. Well, it ain't gonna happen.
Because of that, doing the jhanas is a big big lesson on renunciation. You have to *really* relax the craving, mentally and physically, and the clinging (i.e. the thoughts about attaining jhana). Next time you sit, take the first two minutes and quietly ask yourself, am I wanting
anything right now? Find where in your body there is tension in that, and relax it. (I find this often in my chest, head, and spine. Sometimes I'm leaning forward ever so slightly -- mentally and physically!) Say to yourself, "Let's let that go for just this sitting." Accept whatever is going to happen. Get out of the way. Relax and watch, stay on your object. When you get knocked off your object, relax again, return again. Rinse and repeat.
Sensual pleasures, on the other hand, require no renunciation of anything. There's no lesson in that.
All that said, yes, it's easy to get addicted to jhana. It's a subtler form of addiction, and you're not going to break precepts to keep getting your fix.
(As Thanissaro Bhikkhu says, "Nobody ever killed anyone over jhana."
) But there's still craving and clinging there. Eventually, whatever jhana you're working with gets a little boring, and you develop some dispassion for it.. You relax the craving and boom -- next jhana! And oh it feels so good, it's so awesome, and hey look at me with this attainment!
And there you have the craving to deal with all over again.
In MN 106 I think it was, the Buddha tells Ananda that the 8th jhana, the base of neither-perception-nor-non-perception, is the best object of clinging. So yeah -- getting addicted to the jhanas is just part of the process. But (unlike sensual pleasures) so is not caring if you're going to get them
So how do you get it, without wanting it? Simple -- you set up the conditions for it to happen, and let it unfold on its own. (What are the conditions? Well, that's outside the scope of this particular post...)