FYI: The Parliament of India (at the national level) follows a Bicameral system of legislature.
The constitution of each state in India is determined by the state (within some boundaries). There are some advantages to a unicameral system (simpler, cheaper, less bureaucracy) and some disadvantages (less effective scrutiny, only one system of representation). It has been a matter of the state to decide whether the advantages outweigh the disadvantages. Ultimately this is a matter of judgement.