There are 2 kinds of "losing lanes". The one where its a bad match up and the enemy pushes and gets priority and the one where the enemy has gotten 2-3 kills and is extremely ahead. On the first case, its easy and a jungler should gank to relieve some pressure and possibly get a kill. On the other hand, if the enemy has kills and is a lot gold ahead, then every gank you do there has low possibility for success, the most possible scenarios is either the enemy survives and continues to put huge pressure or he gets more kills. And even if you manage to kill him, it wont make much of a difference. And in the bot lane, ganking when the enemy is far ahead in gold with kills is even more risky. Its not only the gold from the kills, its also the gold from the cs, cause a winning lane in general will get more cs and a death will only grow the gap, and its also the difference in levels, which is a big difference. Also, if the enemy jungler is close, its 100% a lost fight and more kills to the winning lane. And its way better for the jungler to make safer ganks on other lanes.
If you are on a bad match up and you give early kills, its your fault for getting so far behind and for giving any potential ganks a low success rate. And you shouldnt blame your jungler for avoiding your lane. Instead of trying to fight and give free kills, rather turret hug, play and build defensively. And if you push and get camped and give kills its also your fault because, probably, you are pushing without vision. Ive played in both losing and winning match ups. In losing match ups i just hug turret, build defensively and wait for the enemy to gank, so im not giving free kills. But, honestly, if im in a winning lane and have some kills, whenever the enemy jungler comes to gank, i laugh, he is coming to give me one free kill at least. And even if i get killed, it means my team is going to get something else for free and it wont make me lose the top lane anyway.