You might've heard of such concept in software development as "Tech Stack."
Well, it actually IS your project - technology stack defines what tools are used to implement every element of your project, like the ingredients for a dish you're cooking.
Also, you should consider the fact that it's rarely a good idea to choose a backend solution that is written in a programming language that only 5 people in the entire world understand.
Once those people stop working on your project (the reasons might be different), you will face the situation when you'd have to rewrite your entire project from scratch.
If, however, you have an existing product already, it is a good thing to know what tools were used in the past and to adapt.
Basically, the platform can be easily defined by the value proposition and the target audience.