The main reason for using OVM is an economy of scale.
You could put together a SV class based testbench architecture yourself, but:
- It would require you to invest time and resources in doing so, and then maintaining it
- Your verification components would be unusable by other teams within your company (because if you can create a testbench architecture, why wouldn’t they do so as well)
- You would be unable to use verification components and solutions from outside your company
- You would have to train every new engineer joining your company on the testbench architecture
You can argue about whether the OVM is the best technical solution, but it has achieved an economy of scale through inter-operability, allowing people to share verification components and have a common language.
If you are starting from scratch, I would highly recommend that you start with the UVM since that is an extension of OVM and has an even greater economy of scale since it has superceded the UVM. It is also where the investment in EDA tools and VIP is going.