What was rewritten to what?

Question

Programming languages

I hear a lot that some have changed the framework, the second completely the PL, but somehow they tell few details, I’m not sure exactly here you can ask such a question, again which item is most likely not suitable, but ...
1. Was there any experience of changing the PL, changing framework? If yes, what did they change to?
2. Did you change on a combat project or start a new project on a new one?
3. Where did the initiative come from? yourself? superiors? customer?
4. What was the overall profit from everything?
5. what are the pitfalls?
6. Is the initiator/customer satisfied (visitors do not always see that the backend has changed)?
For example, I often hear:
self-written site -> yii/laravel
php -> ruby
​​php -> nodejs
jquery -> vuejs
once heard:
nodejs -> zend
if I ask a question in the wrong place, I will be glad to hear where the format of such questions is.

Answer 1

Even if the language does not change with the format "self-written site -> yii / laravel", then in any case, the conversation is that the site is being created anew. Only business logic is inherited. In the other cases indicated, all the more so, everything starts from scratch.
Most often, they are rewritten only because the old one has ceased to meet the requirements. For example, there was a self-written site that was developed by one person. Then the business logic has grown so much that the initial architecture laid down is not suitable for further development or does not scale well. Then they begin to rewrite on php-frameworks, so that, for example, a development team can develop. Or they generally rewrite it into other programming languages ​​in order to get away from the shortcomings of one language and take advantage of the advantages of other languages ​​/ technologies.
Only management can initiate such a process (albeit more often under the influence of developers), since in the end it is the management that will have to pay for the new development.
The profit is that the creation of a new one will allow you to choose the latest technologies, which means getting the maximum dividends from their use.
There are always a lot of pitfalls and they are mainly related to the fact that when creating a new project, some nuances are forgotten that were created years ago and have already been well tested. And when creating a new project, you can simply forget about them.
And as a result, the customer often loses at first, just because "it used to work, but now it doesn't work." And all because they forgot, did not finish, lost sight of, and so on. But over time, most often everyone understands that the rewriting was not in vain.