It's not that easy! Samsung did try using Tizen OS on smartphones. But poor app support means those efforts failed. There's no point creating an open source smartphone OS against Android unless you're compelled to, like the situation for Huawei.
Yes, I used all four Tizen smartphones (Samsung Z1, Z2, Z3, Z4) and they had a really poor app ecosystem. There were some interesting features that I'd love Android or at least One UI to have.
