It was badly managed by Clegg, with little care of the consequences.
Take the student fees issue for example. Long been a core part of their campaign, many of their MPs had made it one of their priorities. Suddenly because of the coalition that position not only had to be dropped, but completely reversed. Clegg could have come out and said that it was a necessary part of the agreement that he signed up to, or he could have allowed the Lib Dem MPs to have a free vote on it - it almost certainly would have passed anyway. If either of those had happened the blame for the reversal would have been placed entirely at the feet of Clegg rather than the wider party.
The question many voters asked themselves afterwards is that if the party is going to reverse their key policies without a care, just for the opportunity to be in power, why not just vote for the other party anyway?
Of course, the kicking the constituency electorate gave Clegg then led to the waste of space that was Jared O'Mara, so they got a very quick lesson in that the grass isn't always greener...