Usually contracts have clauses about what happens in case of a merger or acquisition [0]. If you are powerful, say a wealthy star or a big corporation, you can push for terms that are favourable to you. If you are not, you have to sign whatever they put in front of you or walk out. I guess in this case, there was a clause in the contract that was most favourable to the company and least to the contributor.

[0] For examples, look at any SaaS company's privacy policy. Here is Figma's:

If we are involved in a merger, acquisition, financing due diligence, reorganization, bankruptcy, receivership, purchase or sale of assets, or transition of service to another provider, then your information may be sold or transferred as part of such a transaction, as permitted by law and/or contract.

https://www.figma.com/privacy/