Just happened to come across this post and was thinking to drop my thoughts here as well.
Although web development always has a sentiment for certain newer language is the future, LAMP has always been the fundamental components for hosting a website, especially for small businesses or organization - the same target audience who would need discourse to grow their communities, and they wouldn’t like the idea having to setup something completely separate from their infrastructure, and we shouldn’t be the ones to judge how they plan to build their infrastructure. There’s always valid reasons for people needing Discourse on LAMP, be as particular as the case may be.
As long as we’re considering from a software development point of view, adding a variant simply means effort and market share, it does not always have to be a replacement for the other language.
Having that said though, there are valid technical considerations regarding the use of LAMP given Discourse has quite a few features that may make use of real-time processing that requires a daemon/runtime to be always there in-memory, while Apache is just fundamentally build different to be more ad-hoc rather than being always there. Some adjustments or mechanisms might work on a completely different foundation to achieve the same user experience.