There are 3 possibilities..
1) Colors wanted to retain Radhika only for the first few episodes for popularity sake.. MATSH is their TRP trump card..Obvious they might have thought of including the lead to enhance the show's poularity
2) Ekta might have had reservations about Radhika's participation in Jhalak.
3) Radhika must have found it stressful to balance between the two shows.