That's also what their customers tend to prefer -- they are often large companies themselves, and they can't drop everything to deal with a breaking change introduced by a vendor. They expect stuff that works to continue to work, and they expect breaking changes to be communicated far in advance so they can make plans to deal with them. That's part of what they are paying for.
What you see as mediocrity is a feature of big companies, not a bug. You can't make all the decisions in a project yourself and expect all of the affected stakeholders and customers to go along with it. Their concerns are often valid and need to be addressed because the project has an impact on the business that other teams don't know about.
Star developers at large companies are the ones who build and manage relationships effectively, so they can deliver on projects that have a big impact on the bottom line, and also do high-quality programming work. If you can do this, you can achieve a lot more with the resources of a large company than you could at a small one.