Ganking a losing lane is HARD, if the enemy already outplayed your laner, he will probably be able to do it again, and that would leave you in a 1 vs 1 with a fed opponent. I used to main jungle (and often stil like to playe there), and what I actually learned from that experience was: when you say you are going to gank, they don't look at the map to se if you are near, they just engage and die, even if yuo clearly say in chat "Wait another 10 sec that I will be there"... too many times I said "Red/Blue then gank" and then, when I reach the buff, I get the "an ally has been slain" and the blame for not ganking him, only to see that my ally died either under the enemy tower, or in the enemy's part of the lane.
When you do get a good gank, they wil just kill minions and won't follow, a losing laner is SCARED of fighting, so he only wants you to get the enemy low enough for them to instakill them, and if you take the kill, you STOLE the kill and you are a bad jungler, so they flame you... on top of that a winning lane will have a better setup for jungler's help, so you will get counterganked more efficiently and easily since the enemy is stronger and probably better than your laner, and let's not forget, a winning laner can ward more safely, so he can have even better awareness than a losing laner, preventing your ganks and making you waste time you could've used for dragon/ganking a winning lane/farm/killing the enemy jungler.
On the other hand a winning lane, for the opposite reasons, will be easier to gank. You will have better support from confident laners since they are already winning, they will probably have more and safer access to vision, making your ganks easier and stronger, the laner(s) will probably be able to handle an enemy gank making a counter-gank easier.
I'm not saying you have to let the lane go from 0/1 to 0/10, but unless the situation is just too good (like the enemy is overextending too much and you're confident since you are fed, or maybe your laner is inclined to help with the gank instead of suiciding and blaming you for not ganking, or better still another laner can come and help) it's better to either farm (and control objectives), or gank other lanes.
Don't misunderstand my words, ganking lanes is as important (if not more important) as getting ahead and taking objective (since succesful gank = easier time taking objectives and better resources to help take them), but ganking a losing lane is usually not worth an objective or farm, since the laner won't cooperate 90% of the time. That said, if the laner i inclined to cooperation instead of just flaming you, things can change, unless you have a better "gank" in another lane, but then the laner should understand, getting a double bot for the adc, is better than making his 0/1 become 1/1.
So, if you're one of the 10% of laners who actually want to cooperate, I guess you've just been unlucky by getting jungler who're fed up with bad laners who want them to do all the job and still take all the credit.
That said remember: a jungler is not a babysitter, he has already too many things to control on his own (objectives, jungle, enemy jungler) to babysitt a laner that only has to focus on his lane and maybe roam a bit (unless he's so strong that the enemy jungler is already shutted down and he can take the luxury of babysitting).