They were fine before that. They were making enough money to stay afloat, but the founder wanted to expand. So he took VC money... and then the VCs began making demands of him. And then Imgur started sucking.
I remember one of the first changes that the VCs forced on them: Imgur debuted a new API, and if you want to access albums through the API, you have to pay a huge amount of money. There were some allowances for small, limited usage for free, but any app published on a major app store would blow past that limit easily. The cost might be fine for a big company, but it screws over one-man operations like...well, like most Reddit apps. The developer of Sync got hit pretty hard by it.