Hecarim in low elo

I picked up the game around 1 and a half months ago and found a great liking in playing hecarim.

Now, after around 200 games or so, ive noticed a trend and i cant seem to figure out what causes it. Even when im ahead in both cs and kills, i still somehow lose games when fed. I obviously know that it sometimes may be due to me not playing out my lead correctly, but what happens most of the time is that my team still refuses to contest objectives with me, even when they have prio after i ganked their lane successfully. Why is this? Ive talked to some friends of mine who usually place anywhere between plat and diamond, and with them i came to the conclusion that most iron or bronze players simply do not know how to play around him when hes on their team. Is this the only problem or, if no, what are other causes for his abyssmal winrate in low elo in general?