Reason behind this is it both has KJE and both are in the Lovers trilogy. Both have different storylines but both have the same sort of meaning behind it.
The story may sound different but I think they have the same concept (rich man falling in love with a poor woman and everyone is against them). They are both SUPER ROMANTIC dramas and the main couples share an amazing chemistry!! In these two dramas you will find nothing but romance, romance and again romance (those are two of the best K drama couples that I've seen) plus both dramas have a crazy jealous fiancé and a love triangle. The only difference is that in LIP the girl isn't sick.