It is not surprising that liberals believed in progress. The idea of progress justified the entire transition from feudalism to capitalism. It legitimated the breaking of the remaining opposition to the commodification of everything, and it tended to wipe away all the negatives of capitalism on the grounds that the benefits outweighed, by far, the harm.
What is surprising is that their ideological opponents, the Marxists - the anti-liberals, the representatives of the oppressed working classes - believed in progress with at least as much passion as the liberals.