1. Even small changes might have ripple effects over the product. Allegedly, Walmart lost $100M within 10 minutes because of a bug in production. It happens quite rarely, but you don't want it to happen. It is like insurance.
2. Speed of change is critical. It helps to move organization forward faster. What if the change is a BLOCKER level security issue and needs to be deployed ASAP?
3. Free your team resources on work on something more meaningful. If your team doesn't need to stop and spend countless hours to do a full regression it disrupts the process and slows down development. They could have done better/more testing of branches/PRs/commits instead.
4. QA happiness. You employ smart people and they already possess a lot of knowledge about your system. You don't want them to leave because they are forced to do tedious click-through instead of interesting meaningful work.
5. You might not be looking to hire more developers in the near term. But I can bet you that you will at least double your development team size within 5-10 years. If you can autoscale regression testing without need to double your team size then an autonomous tool will pay for itself with dividends. It will help to scale more easily AND save money at the same time.