running multiple PHP versions in parallel

This question has been on my mind for quite some time. Although I don't really expect a solution, maybe someone can at least tell me why.

I've been running multiple PHP versions in parallel with mod_fcgid on webservers for a long time. Unfortunately I always had to compile all but one (the "system version") of them myself. I can do that, no problem. I only wonder why there are no PHP packages from "trusted" sources that can be installed alongside each other. I think running PHP as cgi is quite common these days, so having distinct paths for different PHP versions would seem obvious to me. I can see why big vendors (red hat, debian) won't do that, but why don't repositories like dotdeb (debian) or ius (centos) package their PHP versions this way?

Repositories always contain the latest versions for security reasons. That's the short answer really. There are exceptions to every rule of course since there can be multiple "stable" versions of a given software, but usually there's just one because it would be too cumbersome to manage multiple versions.

Besides, PHP 5.5 is the version you should be running, and 5.4 only if you have some applications that require it. 5.3 shouldn't be used at all because it hasn't seen an update in about 6 months and is end-of-life.