SmilingPanda19

Just a concept I was think about:

They never explained why Ursula truly wanted Ariel’s voice. I have a theory for it. (I haven’t done too much research so correct me if I’m off the rails)

It’s assumed that Triton and Ursula are siblings, Ursula being the younger one. It is also believed that their parents are Poseidon and Amphitrite. It’s pretty obvious that Ursula was banished by Triton to the far ends of the seas. 
When she was banished her mermaid tail could have been taken by her mother and replaced by her ugly looks. 
Over several years it’s clear she has had many victims. Why would she do this to them and put them into jars though?

I think it was becoming she gave them  impossible tasks to complete for something they wanted. In signing the contract she asked for something. It could be anything really. Not just a voice. 
In that case, she would have been quite brilliant actually. She already got what she wanted, which was given on the signing of the contract, but she made it appear as if she wants you all together. 
I believe Ariel could have been the last piece to a quite literal puzzle. She stole feet, legs, hair, eyes, ears, etc. from other people, the last thing to take was a voice. Then she could escape her captivity in her deep caverns. She would be able to escape to the land as a human and take over. She would have seen the ships the humans had built and could have assumed the people above were on the edge of ruling the sea and she could finally get what she wanted. 
This could be off the walls, but I was just thinking I guess. 
I think it would be cool to have a villain who took pieces of different people’s identities to build a new one for themself.