Steam is the largest digital game distributor on PC. Developers have direct access to update their games through Steam, so only need to be concerned with their own QA and release procedures.
A hotfix is basically a small patch, generally released relatively quickly to address specific issues. With limited changes compared to the previous release, they can often get away with very focused testing, and skip a lot of the normal release procedure (depending on the nature of the fix, and how likely it is to affect other things).
In addition to the released version of the game, which everyone automatically updates to, Steam also supports different beta branches of the game (essentially updates that have not undergone the full testing procedure). These are optional (can be either public or private) and can be used to give access to new features or balancing changes, etc, before they are made available to everyone. Generally this is to get feedback, stress test new features and collect bug reports from people who don't mind that the changes aren't finished and may not be stable, etc. Rarely, beta branches can also be used to make certain bug fixes available to those who run into them, before they are fully tested and officially released.
Part of the reasoning behind releasing larger updates is efficiency. The full test procedure is fairly involved, especially on consoles, so if possible it is better to include multiple changes and fixes.
Another issue is the risk of introducing new problems. Though generally rare, any update can at least potentially cause new problems (more so with new features or balancing changes, etc, though).
Focus and Sony aren't just waiting for Larian to tell them when to update. Focus has their own release standards and procedures, and makes their own assessment on the severity of issues and the necessity and timing of patches.
Ask Otzi his problems. All of them are solved.
