I bought two brown fig cutting about 4 years ago. Same size, one I put in the ground inside my unheated greenhouse and another in a pot. I covered the one in the ground every winter and it comes back without any die off. but never  produces any figs. I keep cutting it back about 4 feet from the ground. Lots of leaves but never any fruit at all. Its twin has been in a pot that I bring in every winter and it produced a dozen or so very nice figs. I know that having them in pot encourages fruiting but what is happening with the one in the ground? I'm about to give up on it. 

I've had some things like that happen as well. I'm thinking my issues in ground at times have been too much vigor. The larger root system encourages growth at the expense of fruiting. You might try less water and less nitrogen so as to slow growth.

Not sure what zone you are in but what I find instrumental is getting the right fig variety for my zone. 
My select in ground figs have produced very nicely every year for over 20 years.   Last year I took the time and focused on pinching fruiting shoots after 6 leaves and thinned fruit that developed after July and even though it was an off weather year my figs managed to ripen most of the figs.

in summary;
ensure the soil is OK for the figs (PH, organic matter, drainage ...)
grow fig varieties suitable for your area
pinch the fruiting branches 5/6 leaves in June
thin/drop any new fruit that develops after early July
thin any suckers that form or branches that are criss crossing and producing shade.

Happy figging!

Fully agree with Pino's reply. Matching figs to your zone and micro climate very imp to fruiting. Here in Yuma (zone 10) with a very short dormancy period, I find that my varieties, all in the ground & all  having breba crops produce best with moderate pruning that 1) forces breba crops on last years growth & 2) keeps them at a bush size, under 6 feet preferably, with many new branches for main crops. It's to hot here to keep potted plants, long term, but I do pot up, in 5 gal pots, rooted cuttings for givaways and selling as year old starts. My opinion is that too many people focus on "how many varieties" rather than "what works here"

Have you checked the soil that the planted tree is growing in? It could be lacking some nutritions that encourage fruiting possibly.

I agree with Pino.....pinching and thinning will help

Hi louborges,
Why 4' from the ground ? IMO, that is too small 6' or 8' is better.
The potted tree, is she making brebas, maincrops, ot both ?
I would stop trimming the in ground tree. If you want to thin, then remove a branch. Don't cut all branches in half. Trimming is often used to make trees go bushy.
And  I think that your tree is going bushy.
Other question: Does the in ground tree make figlets and they drop ? Does it nether show figlets ?

I have a tree that makes figlets and most (ok, all so far - but this year, 10 fruits are hanging on so far, not holding my breath for that, but holding the axe ) will drop, so if one doesn't keep an eye on her, one could think that she never fruits .
Well indeed, she never fruits because no fruit has ripened until now, but she starts the fruiting process at least.
Fruit drop might be caused by late cold spells, so your in ground has perhaps a problem with the weather - see the remark of Pino, and change for a more adapted cultivar for in ground growing at your location.