Phil Sturgeon wrote a blog post explaining why the recent PSR-7 middleware is useful and can save both frameworks and users a lot of time.
Unlike the way the Ruby and Python communities ability to align on a single solution, PHP needs the elders of the large framework tribes to come together to pick standard interfaces for these things to get the same affect. This in turn pushes large swathes of the community towards a single standard, and if it comes with framework approval people end up using it regardless. Luckily we’re half way to that solution with PSR-7, which specifies interfaces for HTTP requests and responses. Awesome!