He wasn't expected to win the party leadership, being much more to the left than most of his party. Party members voted him in on a landslide.
The party then spent a year trying to oust him from the party, including a huge proprtion of polliticians resigning from his cabinet, this continued until they managed to get another leadership contest.
He won again.
During this the largely right wing press, the not exactly neutral bbc, and the Liberal press shit all over him constantly.
He's made some questionable decisions as leader, and isn't very media savvy, doesnt speak in soundbites, and this reallly doesn't help his cause.
He's approximately 100x a better human being than May, and 100x more likely to keep his promises than the Lib Dems