To add to tdammers' answer...
There are a huge number of companies who insist to build everything from scratch. By doing so, it's likely to be kept private since they consider it their own valuable IP. They pay for all of the development on their internal code-base. There are pros and cons to this.
Open source on the other hand, which may even start out as proprietary, typically has a larger contributor base. This results in a pile of benefits for users, assuming the project is successful:
- More resources have worked on it (more testing, planning, development, support, documentation, etc.)
- Larger talent pool / ecosystem (consider hiring)
- Less training for new hires
- Less maintenance
Effectively you can delegate a large portion of your code-base to the free community, which, if the community works, is a lot more powerful than your own small team. It also adds the risks of too many eyes (more vulnerabilities found - which can be seen as good or bad).
It doesn't make sense to have commercial frameworks in PHP. PHP is open source by nature, so any commercial projects always seem a little foreign and it adds too much barrier to entry. A commercial framework may be good, but it's very high risk for anyone to use without some serious backing. The size of a project's community usually comes across as security or longevity. Additionally, without a large community backing, the company releasing it will likely gain very little.
Hope this helps.