Here is a discussion exactly about "Why mixing templates and logic is not necessarily bad": http://www.thisisvoid.org/article/03

I have a math research background: if you can prove something in 2 pages with no extra tool, it's far better than doing the same by invoking a big difficult Theorem.

Moreover, I am not a profesionnal developer. And for me, installing Apache+PHP is enough. I don't want to add more tools, more layers. The list could be endless: Let's use Symfony, Composer, Brew (random name here, I don't know what is Brew)... and at the end I'll have a big big thing...

I really want to keep it simple...

Each new layer is like "minus 10 points" for my project ;)