Firstly, Anika was forced into this marriage, so their marriage isn't legal. If Anika wants, she can actually file a case against Shivaay, but she won't do that, and she wants to get out of this marriage.
But the thing is Shivaay and Anika are not legally married, and if you go by witness, Tia has become Shivaay's legal wife because...
Normally, how marriages are legalized in India when people get married in religious way is that, whoever conducted the marriage, i.e Pandit, Islamic or Christian Priest, would give a document/certificate, which states that this guy and this girl got married on this date and day, under this religious institute and with these witness. That document, you need to submit at the registrar's office and along with an application for marriage certificate. Then the bride and the groom has to go and sign on the register there and a marriage certificate will be issued, legalizing your marriage.
And in case, if a couple don't have a legal document certifying their marriage, then the court would call for witness who have attended the wedding.
So if we go by that, then apart from Shivaay's family and Tia, Robin and her mother, not body has seen Shivaay marrying Anika or saying that they got married.
Shivaay married a veiled girl, and the next day newspaper had their wedding photo with the news that Shivaay married Tia. Then Shivaay calls media and officially introduces Tia as his wife.
So, Even if Shitia doesn't marry ever, Tia can still claim that Shivaay is her husband with thousands of witness (media, people who saw the news, guests at the function and the Pandit who conducted the wedding) while Anika has no proof unless The Oberoi family decides to go against their son. In such a situation, where there is no legal documents or witness which can say Anika and Shivaay are married, and there are proofs that Shivaay married Tia. Shivaay being a businessman, why is he thinking of divorcing Anika, and actually legalizing a marriage he wants to end/dissolve? He can very well, go on with the normal legal marriage steps and legally marry Tia, as he himself claimed that he doesn't consider his marriage with Anika. And Anika also doesn't want to stay with Shivaay, and that marriage itself is illegal.
Why is the biggest businessman in India, not going the most practical, easy and best way? Why is he going the complicated way and exposing his truth?
Sorry, if I didn't make any sense